Spinoza defines idea in E2def3: “By idea [ideam] I understand a concept of the mind which the mind forms because it is a thinking thing.” Spinoza explains the use of “concept” (conceptum) as follows: “I say concept rather than perception, because the word perception seems to indicate that the mind is acted on by the object. But concept seems to express an action of the mind” (E1def3exp).

This definition with the explication is a bit difficult because Spinoza also divides ideas into actions and passions (E3p1). Passive ideas are formed in us because we are being externally affected, whereas active ideas are due to us. But here, in E2def3, Spinoza seems to say that any idea is formed by the thinker, which might be taken to mean that any idea is actively formed by the mind. Arguably, E2def3 says that the function of the mind is to affirm what is the case. In perception, human beings see, hear, feel what is taking place, and such affirming what is taking place is the work of the mind. When the idea is a passion, it is externally caused. For example, I look out of the window and I see Peter walking. My body is affected in a certain way and my mind is aware of that. My mind forms the idea of Peter walking. In active ideas – or equivalently, adequate ideas – the mind is also responsible for what is thought about. For example, in geometry, the mind follows the eternal order of space. This kind of idea formation does not depend on the thinker being affected but on the thinker as a reasoning agent.

As already stated, the activity involved in an idea is for Spinoza affirmation. Affirmation, conceived abstractly, is something that is predicated of all ideas. This is a much-discussed issue in Spinoza scholarship because Spinoza also equates “will” with affirmation, and in this way parts company with what could be called Descartes’s belief-voluntarism. For Descartes, belief consists of an idea and an action. Ideas in themselves just propose something to the mind and an act of assent is required for a belief to be generated. “The intellect puts something forward for affirmation or denial,” Descartes writes in Meditation 3 (AT7.57). Spinoza sees the relation between intellect (idea) and will (affirmation) differently. For him the affirmation lies in the idea. Believing for Spinoza is not voluntary nor is it free as Descartes thought. Spinoza, then, identifies will with the intellect.

Spinoza has a notorious argument for the will’s identity with the intellect. Let us call it the WILL=INTELLECT argument:

Spinoza refers here to E2a3. This axiom tells that there are modes of thought which cannot be conceived without ideas, even though they are not identical with ideas. For example, a desire is something that cannot be conceived without the idea of what is desired, but the idea involved in the desire can be conceived without the desire. For example, my desire to drink a glass of water cannot be conceived without conceiving my drinking a glass of water. However, my drinking a glass of water can be conceived without conceiving the desire to drink. The argument in E2p49d is that an idea of x cannot be conceived without affirmation and affirmation cannot be conceived without x. Affirmations do not modify ideas the way desires do.

The argument is rather straightforward. Let us say that A is the idea of a triangle having its three angles equal to two right angles, and B the affirmation that the three angles of a triangle are equal to two right angles. It is clear that B involves A. Such an affirmation cannot be without the corresponding idea of the triangle. Moreover, it is equally clear that the idea of a triangle having its three angles equal to two right angles involves the affirmation that the three angles of the triangle are equal to two right angles. It is impossible to think of the triangle as having its three angles equal to two right angles without affirming of the triangle the property of having its three angles equal to two right angles.

More generally we can present this as follows. Let us suppose that I(x) is the idea of x, and C(Ix) is affirming what the idea represents. What Descartes says is that the identity, I(x)=C(Ix), does not hold, whereas Spinoza says it does. Descartes perhaps would defend the non-identity by saying that intellect can present to the will an idea without the will accepting it. Thus, affirming an idea cannot be identical with the idea. Many of the ideas we have are not such that we believe them. How would Spinoza respond?

Unlike Descartes, Spinoza does not hold that affirming something and believing it are identical. A plausible way to see the relation between believing and affirming is that an affirmation, that is, an idea, is a belief if there is nothing that prevents the affirmation from being a belief. For Spinoza, suspension of judgment happens in a situation where someone “sees that he does not perceive the thing adequately” (E2p49s). Spinoza gives an illustrative example which can be called ”The Child and the Horse”:

Spinoza’s point here is that to doubt what is given requires an idea which makes the given information possibly false: doubt requires a reason for doubting. Here the child is supposed to have only the idea of the winged horse before her mind and so she has nothing on which to build the doubt.

However, it almost goes without saying that sometimes we suspend judgment and, as already pointed out, Spinoza does not deny that. We do not believe that all our ideas are true. However, how is suspension of judgment possible if ideas essentially involve affirmation? In order to make such suspension possible, Spinoza has to think anew how affirmation is related to belief.

A plausible line of reading Spinoza is to attribute to him a distinction between existential beliefs and beliefs about the given. To understand this, let us modify the “Child and the Horse” example so that the child firmly believes that there are no winged horses. Now she has an experience of a winged horse, but she does not believe that such a horse exists. Spinoza would say that the child affirms wings of the object she is in touch with, but this is not to say that she has to believe in its existence. Suppose that later she is asked by someone whether the horse she experienced really had wings or whether there was just some dust surrounding the horse in a suitable way. This question makes sense and we may suppose that the child still insists that the horse had wings even though she does not believe in its existence. The idea as long as it is real does not lose its affirmative nature. But this is not the same as saying that the thing the idea is about has to be taken to exist.

Let us consider an example from Spinoza’s correspondence where he reports of a strange experience, call it “Spinoza and the Brazilian”:

Here Spinoza knows that the Brazilian he was hallucinating did not exist. However, this does not prevent him from giving a description, true or false, of that non-existent thing. The interesting thing is what it is to take an experience as an experience of something that exists. How does such an experience differ from an experience which is known to be unreal? Is the predicate “exists” or “real” added to such experiences? Perhaps not primarily. Perhaps, the difference is that the experiences taken as real are such that they become relevant to behavior, to what we do. In knowing that he hallucinates, Spinoza does not, not at least seriously, ask what the Brazilian is doing in the bedroom.

Finally, let us turn to the ontology of ideas and their objects. In E2p7s Spinoza endorses the thesis that an idea of a mode is identical to that mode:

This identity thesis has been studied a lot. It gives Spinoza’s conception of how our ideas and our minds, as ideas of our body (E2p13), are related to the physical world (Extension). One way to read it is that modes and ideas of those modes are numerically identical. And their numerical identity means that any thing in our world can be identified both by using mental predicates only and by using physical predicates only. This is a kind of double-aspect theory. The double-aspect theory is problematic because Spinoza believes that ideas can be caused by ideas only and bodies by bodies only. Suppose now that body B causes body B*. The double-aspect theory says that B is identical to some idea I. But, then, because B causes B*, and B is identical with I, I should cause B*. This would be against Spinoza’s basic commitment that causation occurs within an attribute (see E2p6.)

Another way to read Spinoza’s identity theory is to call on Descartes’s two senses of idea (AT7.8) to help:

• Sense 1: Idea taken materially as an operation of the intellect.

• Sense 2: Idea taken objectively as the thing represented by that operation.

Given this, it seems natural to hold that Spinoza’s identity theory says that the idea only taken objectively is identical with its object. This reading is natural because (i) in E2p13 Spinoza tells that the object of the human mind, that is, of an idea, is the human body, and (ii) in E3p2s Spinoza infers from the identity thesis that the human mind is identical with the human body. Here the identity thesis is used to show that an idea and its object are identical. However, if the identity between ideas and their objects were all Spinoza had to say about the relation between mentality and physicality, he could be read as some kind of reductionist: the mental realm is constituted by ideas as representations and they are identical with bodies that constitute the physical realm (and vice versa).

Ideas in Sense 2 depend on ideas in Sense 1. Thus even though the ideas in Sense 2 are identical with bodies, that is, modes of extension, this does not mean that mentality disappears from Spinoza’s universe. There is the infinite thinking power of God which guarantees that every body that is, is thought of. And this means that every body that is exists also as an idea, because in Sense 2 a thing is an idea just in virtue of being thought about. Being an idea in Sense 2 is for Spinoza, because of the realism he commits himself to, an extrinsic denomination of bodies.

Spinoza is not so explicit that he has a concept similar to idea in Sense 1. However, in E2p2d, where Spinoza argues for Thought (cogitatio) being an attribute of God, “thoughts [cogitationes]” and not “ideas” are used. Cogitatio in Latin seems to be a rather good term to refer to an operation of the intellect, that is, to idea in Sense 1. Its first meaning, given by Lewis and Short in their Latin Dictionary, is thinking and this dictionary also tells that Cicero, who influenced Spinoza in his terminological choices, used cogitatio “as an intellectual power, the ability of thinking, power or faculty of thought, the reasoning power.” In the Oxford Latin Dictionary, the first meaning of cogitation is “The act or process of thinking, reflection, thought.” Thus, in E2p1d Spinoza seems to use cogitatio in the sense of an operation of the intellect (idea in Sense 1).

Like most philosophical labels, ‘idealism’ means different things to different people. Often the term describes metaphysical systems in which reality is somehow thought-dependent. Whether Spinoza is an idealist in this priority-of-thought sense (either intentionally or as a result of the poverty of his philosophical resources) has been a point of contention since the nineteenth century.

Historically, this debate has run in tandem with a debate over Spinoza’s alleged denial of the reality of all metaphysical diversity – that is, over what we’ll call here ‘Parmenidean’ readings of Spinoza. Parmenidean readings can be classified as ‘idealist’ not only in virtue of the historiographical identities of their original proponents (German and British Idealists), but also insofar as such readings regard all multiplicity as mere projection of finite thought. Prima facie, Spinoza’s writings portray a universe maximally rich in ontological diversity: God is a “substance consisting of an infinity of attributes” (fundamental, qualitative ways of being) (E1def6), from which “infinitely many things in infinitely many ways” follow (E1p16, alt. trans.). But, on Parmenidean readings, it is only to our limited minds that substance appears under diverse attributes, or gives rise to an infinity of “modes” (dependent beings). In this entry, we address both controversies, starting with the question of the priority of thought.

Priority-of-thought readings regard Spinoza’s metaphysics as “lopsided” (Bennett Reference Bennett1984, §16.3; cf. Caird Reference Caird1888, 156), insofar as Thought appears to be ontologically and explanatorily more fundamental than any other attribute. Such readings are encouraged already by the Ethics’ opening definitions. An “attribute” is “what the intellect perceives of a substance, as [tanquam] constituting its essence” (E1def4; cf. Ep9, iv/46). That definition’s reference to “intellect” has baffled many readers. (Why not define an attribute simply as “constituting substance’s essence”?) For if there can be no attribute without an “intellect” to “perceive” substance, the essence of any attribute will involve a relation to Thought. Distinctions between different attributes will seem to reduce to distinctions between ways of thinking of substance. (To quote Pollock, “Thought swallows up all other attributes; for all conceivable attributes turn out to be objective aspects of Thought itself,” Reference Pollock1899, 168.) Indeed, Spinoza’s official argument for God being “extended” turns on all bodies “involving” (implying) the same “concept” (E2p2d; cf. Newlands Reference Newlands2011). That is, Extension seems to be ascribed to God based on considerations about Thought. Combined with Spinoza’s insistence that any attribute is essentially conceptually self-sufficient (E1p10), the conclusion that all attributes depend on Thought suggests that Thought is the only genuine attribute (e.g., Martineau Reference Martineau1883, 188). Spinoza claims further that it’s evident from the definition of attribute that “the more reality or being a thing has, the more attributes belong to it” (E1p9). It seems difficult to ask for a more idealism-friendly conception of “reality” than one on which its degrees track diversity in ways something can be thought.

It’s true that for Spinoza “intellect” picks out only veridical thought. So if an intellect perceives substance as Extended it genuinely is Extended. This rules out so-called ‘subjective’ interpretations of attributes (e.g., Caird Reference Caird1888, 142–51; Wolfson Reference Wolfson1934) on which they are mere appearances or projections of finite minds (a reading encouraged by translating tanquam as “as if” in E1def4). Still, by E1def4, availability to (veridical) thought seems part of the essence of any attribute. Moreover, it’s not only the notion of attribute that is grist for the idealists’ mill. Substances and modes are also defined in part by how they are “conceived” (E1def3,5). From here, it’s a short step to the conclusion that all ontological variety is merely ideal – constituted by and within thought.

It’s unclear how to square this apparent explanatory and metaphysical privileging of Thought with Spinoza’s equally explicit commitment not just to the conceptual (and so also causal) self-sufficiency of each attribute (E1p10), but also to the equality and parity of all attributes in relation to substance, and, finally, to the equinumerosity of their modes (e.g., Caird Reference Caird1888, 150; Melamed Reference Melamed and Goff2012e; Newlands Reference Newlands2011). Spinoza insists that “all the attributes … have always been in [substance] together”; “each expresses the reality or being of substance” (E1p10s), and that all manifest the same “order and connection” of modes (E2p7s).

Some readers propose that we can avoid inconsistency with these commitments and idealist ‘lopsidedness’ more generally by distinguishing the attribute of Thought from some other sense of “thought” or “intellection.” Deleuze (Reference Deleuze1990) distinguishes between Thought as an attribute and substance’s “power” of thought, which Spinoza describes as “equal” to substance’s power of producing things (E2p7c). Newlands (Reference Newlands2012) proposes that “conceiving” should be understood as an attribute-neutral, “structuring” relation, irreducible to “mental” actions specific to the attribute of Thought. Others still point out that there are equally reasons to see Extension as the attribute prioritized by Spinoza. For example, human minds seem to depend for their existence, individuation, and degree of power on the bodies that are their intentional objects (E2p11–13, E3GDA; cf. Koistinen Reference Koistinen and Della Rocca2018; Hübner Reference Hübner2022b). If we emphasize this part of Spinoza’s picture, he begins to resemble a materialist rather than an idealist (cf. Nadler Reference Nadler2008a, 597; Curley Reference Curley1988, 74–78).

Let’s turn now to ‘Parmenidean’ readings, on which the prima facie richness of Spinoza’s universe – the multiplicity of attributes and modes – turns out, or threatens, to be illusory. Depending on the readers’ commitments, this outcome is either a failing of Spinoza’s system (so Hegel, Joachim, Caird, and Martineau) or its profound insight (Della Rocca Reference Della Rocca, Förster and Melamed2012).

Traces of a Parmenidean reading are found already in Leibniz, but it is associated foremost with Hegel. According to Hegel, nothing exists in Spinoza’s view except substance as undifferentiated being (“The true is simply and solely the one substance … this constitutes the Idea of Spinoza, and it is just what τό σν was to the Eleatics,” Reference Hegel, Rockmore, Haldane and Simson1995, 256–57; cf. Caird Reference Caird1888, 142–46). So understood, Spinoza would offer no answer as to how the “many” could be reconciled with the “One,” a worry central to many Idealists (e.g., Joachim Reference Joachim1901, 103; Caird Reference Caird1888, 152–53; Martineau Reference Martineau1883, 185–88; cf. Newlands Reference Newlands2018).

Hegel’s interpretation may seem to force Spinoza into categories foreign to him – he is made to represent the limited standpoint of the “understanding” that grasps only the “abstract universal” (Hegel Reference Hegel, Rockmore, Haldane and Simson1995). But the demand that the existence of anything in any way distinct from substance be explained by the nature of substance is well grounded in Spinoza’s own commitments: to universal intelligibility (E1a2, E1p11altd), and to the explanatory priority of substance (E1p1) (cf. Caird Reference Caird1888, 141–42). The basic contention of Parmenidean readings is that Spinoza fails to live up to his own explanatory commitments.

But there are different kinds of more specific Parmenidean conclusions one could draw. First, whereas priority-of-thought readings make Thought into the only attribute, one could deny that substance has any attributes (e.g., Hegel Reference Hegel, Rockmore, Haldane and Simson1995, 268–69; Della Rocca Reference Della Rocca, Förster and Melamed2012). Next, one could deny that substance produces any modes, finite or infinite. But it is neither attributes nor modes simpliciter that typically take center stage in Parmenidean readings. The most heated disputes concern the reality of finite modes like ourselves. Following Hegel and Maimon, the view on which Spinoza denies the reality of finite things is usually dubbed “acosmism” (since it denies the existence of a cosmos – a “world” or “universe”); only God remains (Hegel Reference Hegel, Rockmore, Haldane and Simson1995, 281–82; Maimon Reference Maimon, Melamed, Socher and Reitter2018, 64). Some acosmic readings target only certain aspects of finite modes (e.g., their passivity, Della Rocca Reference Della Rocca2008b), with the result that finite things exist only partly or to a degree (e.g., Joachim Reference Joachim1901, 112; Della Rocca Reference Della Rocca, Förster and Melamed2012). Other readers worry that there is no room for finitude at all in Spinoza’s system. (As Caird writes, finite things seem to “have no existence at all … they are mere creatures of the imagination,” Reference Caird1888, 163–65; cf. Hegel Reference Hegel, Rockmore, Haldane and Simson1995, 258, 281). It’s not clear how to articulate such a position coherently, since the finite minds allegedly responsible for the illusion are themselves illusory (Joachim Reference Joachim1901, 112; Caird Reference Caird1888, 170).

There are different ways to make a case for one of the above Parmenidean conclusions, but let us note, first, some argumentative nonstarters. To begin with, one cannot conclude from Spinoza’s substance monism alone that modes are unreal. That would be to confuse non-fundamentality with unreality: modes, like properties, aren’t substances, but this doesn’t mean that they are nothing. Likewise, one cannot infer the absence of distinctions from Spinoza’s denial that substance is “divisible” (E1p12–13). Neither modes nor attributes are “parts” of substance. (There are also argumentative nonstarters for the opposite camp: if the question is not merely of Spinoza’s intentions but also of the conceptual resources of his metaphysics, merely enumerating passages expressing a prima facie commitment to diversity won’t defeat Parmenidean readings. The question is not merely of what Spinoza says but also of what he is entitled to say.)

A more promising way to try to establish a Parmenidean conclusion is to contend that Spinoza fails to successfully demonstrate the necessity of any distinctions. (Hegel for instance complains that these are “only assumed and presupposed from the ordinary conception … Were [they] to be justified, Spinoza would have to deduce [them] from his Substance, but that … comes to no vitality, spirituality or activity,” Reference Hegel, Rockmore, Haldane and Simson1995, 288; cf. Hegel Reference Hegel1969, 536–37; Martineau Reference Martineau1883, 179–82, 204–09; Caird Reference Caird1888, 142, 152, 172–74, Joachim Reference Joachim1901, 103–08.) But this charge can strike one as unfair. After all, Spinoza formally demonstrates that God must have the attributes of Thought and Extension (E2p1–2) (although since those arguments appeal inter alia to our experience of finite thoughts and bodies, their success rests in part on a prior refutation of acosmism). Spinoza undertakes to formally deduce the necessity of modes as well, arguing that “From the necessity of the divine nature there must follow infinitely many things in infinitely many ways, (i.e., everything which can fall under an infinite intellect),” on the grounds that the “more essence or reality” a thing has, the “more properties” can be “inferred” by an “intellect” from its definition (E1p16, alt. trans.; cf. Martineau Reference Martineau1883, 194–95). Unfortunately, it’s not clear why we should accept this reality-to-properties principle, and Spinoza says little in defense of it against Tschirnhaus’s worry that it seems false (Ep82–83). Hegel objects further that Spinoza fails to show that substance gives rise to modes of its own necessity, without the mediation of an “external intellect” (Reference Hegel1969, 113, 536–38; Hegel Reference Hegel, Rockmore, Haldane and Simson1995, 258; cf. Newlands Reference Newlands2011). Parkinson counters that Hegel “overlooks the essentially dynamic character of Spinoza’s substance,” pointing out that in Ep81 Spinoza himself wages an analogous criticism against Descartes’s “quiescent” conception of Extension, which requires an “external,” divine cause of motion (Reference Parkinson1977, 458).

Other readers have tried to defend Spinoza against the charge of failing to prove the necessity of modes by offering alternative demonstrations. Here are just three examples. First, Hübner (Reference Hübner2016) argues that the existence of Spinozistic substance already entails the existence of both the attribute of Thought and of an infinite mode of Thought, since substance is essentially “conceived in itself,” that is, the object of at least one necessarily actual idea. Second, Melamed (Reference Melamed2012d) argues that for Spinoza, God’s essence is necessarily “active,” or a causal “power,” such that God must produce other things. Arguably, however, since Spinoza ascribes activity or causal “power” to God’s essence in part on the grounds that infinitely many things follow from that nature (E1p34d), we cannot, on pain of circularity, use this ascription to establish the existence of those things. Moreover, God essentially being a causal “power” seems consistent with only God existing: in this scenario God’s essence still causes God’s existence. Melamed Reference Melamed and Goff2012e argues that if God were a cause only of himself, God would be equally passive and active; but it is only passivity in the sense of being determined by an external cause that Spinoza regards as incompatible with God (E3def2; Zylstra Reference Zylstra2020.) Finally, one could also try to demonstrate the necessity of modes on the grounds of God’s “absolute infinity”: if there were an attribute or mode that could exist but didn’t, God would (the argument goes) be limited in some way, and so not “absolutely infinite.” Hence God’s nature requires the existence of everything possible. Unfortunately, as a refutation of Parmenidean readings, this argument seems to beg the question, since it simply assumes that something modally or conceptually distinct from God is metaphysically possible. But, unlike Leibniz for example, Spinoza doesn’t allow for natures or essences possible in themselves. What’s possible is a consequence of divine nature (cf. E1p25).

Upping the ante, proponents of Parmenidean readings can argue that the existence of distinctions is not just inadequately demonstrated by Spinoza (the charge we have been examining thus far), but impossible by his own lights. There are two prominent arguments in literature purporting to show that finite things at least cannot follow from substance, and hence that our experience of them is indeed illusory. First, Spinoza is explicit that anything produced by an infinite cause must also be infinite (E1p21–22). Hence, “to account for the existence of [a finite] thing we must take for granted the existence already of another” (Martineau Reference Martineau1883, 203–04; cf. Caird Reference Caird1888, 165–66). Realists about finite modes retort that these follow from God’s nature collectively as an infinite mode (e.g., Garrett Reference Garrett, Förster and Melamed2012; Shein Reference Shein2020). The second argument for the impossibility of finite modes turns on Spinoza’s association of finitude with non-being. He writes, for example, that “being finite is really, in part, a negation, and being infinite is an absolute affirmation of the existence of some nature” (E1p8s1; cf. E1def2; Ep50, iv/240; Ep36, iv/184). For many readers, this association of finitude with non-being suggests that only substance, whose nature is free of limits, is real in Spinoza’s view, while finite individuality is an illusion stemming from an inadequate grasp of substance’s entirely “positive” and infinite reality (Joachim Reference Joachim1901, 105–08; Caird Reference Caird1888, 123; Martineau Reference Martineau1883, 205).

However, this inference from an association of finitude with negation to acosmism is arguably too quick. Spinoza’s writings suggest that finite things are indeed individuated relatively to other finite things (E1def2, E1p28): a given body is a determination of an infinite Extension, and it is not other finite bodies. But this doesn’t yet mean that the nature of a body is not constituted by anything ‘positive’ – that is, by no property or “perfection,” however limited. In other words, we cannot infer from x being limited or determined by y that x is nothing at all (cf. Stern Reference Stern2016). Spinoza’s proto-Hegelian insight is that finite things are understood only when they are related to other things and ultimately to an infinite whole (Caird Reference Caird1888, 142; Stern Reference Stern2016; Shein Reference Shein2020). Indeed, we shouldn’t expect a more self-sufficient kind of existence from a “mode,” that is, from what essentially exists in and is understood through something else (E1def3).

Furthermore, it’s not obvious that what we conceive by means of negating something else cannot also be conceived without negation, on analogy with attribute, which we can conceive as “infinite in a kind” both by “deny[ing]” of it all other attributes and by conceiving of it as “expressing essence” (E1def6; Hübner Reference Hübner and Melamed2015c). Lastly, we shouldn’t forget that negation is only “part” of what makes a finite thing that thing (E1p8s). The other “part” of a finite thing presumably includes its essence under an attribute, which, like any “essence,” posits the thing’s existence, and never takes it away (E3p4d). (Some have argued that this remaining ‘positive’ part is instead the “infinite aspect” of finite things, that through which they affect the totality of other finite things, Shein Reference Shein2020; cf. Caird Reference Caird1888, 171–73; Martineau Reference Martineau1883, 209; but this solution doesn’t seem to save finite things qua finite from acosmic fate.)

Finally, a critic of Parmenidean readings might object more generally to the assumption that Spinoza’s commitment to intelligibility means that he must offer a priori proofs of the necessity of diversity (cf. Pollock Reference Pollock1899). Despite his reputation as a follower of Euclid, Spinoza is clearly open to empirically grounded premises and arguments (e.g., E2a4, E2p1d; cf. Shein Reference Shein2020). Here the debate over the reality of things intersects with the debate over the nature of Spinoza’s commitment to intelligibility and the kinds of explanations he would accept.

Spinoza’s doctrine of ideas of ideas complements another doctrine developed in Part Two of the Ethics, the doctrine of the parallelism of ideas and bodies. Spinoza argues that in God (conceived as thinking substance), there are necessarily ideas of God’s essence and of everything following with necessity from God’s essence (E2p3), where the “order and connection” of these ideas “is the same as the order and connection of things” (E2p7). There is a parallelism of ideas and bodies: there are, in God, ideas of everything following from the attribute of Extension, and the order and connection of these ideas is the same as the order and connection of bodies. Since there are also ideas of everything following from the attribute of Thought, there is also a parallelism within Thought. This is to say that, in God, there is an idea of each idea, and the order and connection of these ideas of ideas is the same as the order and connection of the ideas of bodies: the idea of the idea of a body follows in God and is related to God in the same way as the idea of the body (E2p20).

The parallelism of ideas and bodies is central to Spinoza’s account of the union of the human mind and body (E2p13s). “The object [objectum] of the idea constituting the human mind is the [human] body” (E2p13), and the mind and body are “one and the same thing” conceived under different attributes (E2p7s; for recent discussion, see Hübner Reference Hübner2022b). The parallelism within the attribute of Thought is central to an account of a kind of unity within thought. The “idea of the mind is united to the mind in the same way as the mind is united to the body” (E2p21); the idea of the mind and the mind itself are one and the same thing conceived within thought (E2p21s).

It seems that ideas of ideas are introduced to account for the distinctive reflexivity of thought: any thought can itself become the object of thinking. A mind thinking about bodies or affections of bodies can also think about its own thinking about bodies. It can, for example, think about a representation of a body as a representation, and consider whether that representation is adequate, or has all the “intrinsic denominations of a true idea” (E2def4). Or the mind may think of some idea as a particular kind of thinking activity, categorizing the idea as, say, an instance of “loving” something (see E1a3). Or the mind may, more generally, think about itself (E2p23, E3p9d), perhaps even eventually understanding itself sub specie aeternitatis as a mode in God (see E5p30).

There is some debate about how to understand the details of the doctrine. One could suppose that there is a distinct, higher-order idea for every idea; one might even suppose that in the case of adequate ideas, there is an infinity of higher order ideas, since “as soon as someone knows [scit] something, he thereby knows that he knows it, and at the same time knows that he knows that he knows, and so on, to infinity” (E2p21s; for discussion, see, e.g., Curley Reference Curley1969, 144–50, and Morrison Reference Morrison and Melamed2017, 66–68). Yet one could also take the idea of the idea and the idea to be two aspects of the same mode of thought. In saying that the idea of the idea is “nothing but the form of the idea insofar as this is considered as a mode of thinking without relation to the object [objectum]” (E2p21, my emphasis), perhaps Spinoza is echoing the Cartesian distinction between an idea taken formally and an idea taken objectively (see Primus Reference Primus and Melamed2021a, 266–67). If the idea of the body represents the body as something formally real, or actual, in Extension (E2p11, E2p13), the idea of the idea of the body represents the body as something objectively real in thought. Ideas differ in the bodies (or affections of bodies) they represent, but if we bracket these objecta and focus just on the ideas of ideas, we can see what is distinctive about the reality of ideas: not only do they represent other things, but they also represent whatever is represented as in thought (cf. AT7.160).

Some scholars take the doctrine of ideas of ideas to be crucial for Spinoza’s account of consciousness, but whether the doctrine in isolation could provide (or was even intended to provide) a complete account of consciousness is disputed.

Imagination (imaginatio, imaginari, imago) is an equivocal term with which Spinoza refers to (1) perceptual states, (2) inadequate ideas, or (3) mental images used in thinking.

In his early TIE, Spinoza uses the terms “imagination” and “intellect [intellectus]” disjunctively: imagination produces confused ideas, whereas the intellect produces clear and distinct ideas (ii/28/14–26; cf. Ep37, iv/188/33–189/4):

Most objects can be imagined, as well as understood (intelligere) (TIE[74], ii/28); but there are some objects that can only be imagined, and some that can only be understood. Because the contents of imaginations and intellections are determined by different processes, not all objects can be represented by these two completely different modes of presentation (TIE[86], ii/32). Since Spinoza’s position on this specific point arguably hasn’t changed much in the course of his philosophical career (more on this below), we can use much later texts to illustrate this claim: God can only be understood, not imagined (Ep56, iv/261), whereas beauty, warmth (E1app, ii/82), contingency (E2p44c1), divisibility and corruptibility (E1p15s), sadness, and evil (E4p68) can only be imagined.

In CM, Spinoza describes imagination as the representation of objects based on the mind’s awareness of brain states:

Since imaginations are not direct representations of external causes, but mediated through representations of brain states, imaginative processes can be a source of error: they have us affirm the existence of non-beings. An example for such a mistake is the concept of vacuum, which involves the reification of nothing (i/268). However, as becomes clear from a later passage, imagination also limits the scope of error, since logically incoherent objects – such as chimeras and square circles – cannot be imagined (i/241/9–16).

In Spinoza’s mature Ethics, the terminology of the imagination is used in two ways. On the one hand, the verb imaginari denotes the cognitive psychological process underlying all sorts of sensitive or perceptual experience. On the other hand, imagination is also the name of a kind of knowledge, uniting different kinds of unreliable cognitions under a common heading. Although these two usages or senses of imaginatio are interrelated, arguably they must be kept apart, or else one cannot account for the explanatory role that the notion of the imagination plays in all those passages that are not, or not in the first place, to assess the adequacy of ideas, but to explain certain emotional, social psychological, and political phenomena. According to the first sense, the “imagination is an idea by which the mind considers a thing as present (see its definition in 2p17s), which nevertheless indicates the constitution of the human body more than the nature of the external thing” (E4p9d). According to E2p17s, referred to just above,

This definition of imagination is derived from a more general claim:

Underlying this notion of the process of imagination is thus a view of how people cognize the affections of their body: the idea of the affections of one’s own – or, which amounts to the same here: human – body “must involve the nature of the human body and at the same time [simul] the nature of the external body” (E2p16). Hence, in the basic mental process constituting the imagination, three objects – the nature of the external body, the nature of the subject’s body, and the affection of the subject’s body – are thought of as one.

Since the process of imagination results in confused representations, imaginative processes are not very reliable ways of knowing things. Spinoza illustrates this with the example of Peter’s idea of his own body and Paul’s idea of Peter’s body. Clearly, these are two different ideas at least insofar as they are formed by different subjects. As such, they relate to two different affections: the former “constitutes the essence of Peter’s mind” and represents the affections of Peter’s body, whereas the latter “indicates the condition of Paul’s body more than Peter’s nature.” As a consequence, Paul’s idea of Peter’s body can survive Peter’s death, since “that condition of Paul’s body [which corresponds to Paul having an idea of Peter’s body] lasts” and therefore “Paul’s mind will still regard Peter as present to itself, even though Peter does not exist” (E2p17s) The way in which imagination as a process works explains the epistemic unreliability of imaginative ideas: Paul can imagine Peter’s body as existing even after Peter’s body ceased to exist. By contrast, there is a necessary link between Paul’s idea of Peter’s body and the existence of Paul’s body: Paul cannot imagine Peter’s body as existing, unless Paul’s body exists (E5p21).

A further source of epistemic unreliability of imaginative processes stems from the “association [consuetudo]” of images in the brain reflecting the personal histories of individuals: “If the human body has once been affected by two or more bodies at the same time, then when the mind subsequently imagines one of them, it will immediately recollect the others also” (E2p18). These associations of brain states correspond to associations of imaginations in the mind, which play an important role in shaping the experience of human subjects. The way in which the individual human body has been affected by external bodies, determines which ideas the human mind thinks together, even if there is no actual connection between the objects of the associated ideas. Such associations between imaginations constitute human memory, which “is nothing other than a certain connection of ideas involving the nature of things which are outside the human body – a connection that is in the mind according to the order and connection of the affections of the human body” (E2p18s). For example, if someone is acquainted with workhorses but not with warhorses, the imaginations of horse-related phenomena are associated in her mind with the imagination of the workhorse. Therefore, when she sees the traces of a horse in the sand, she considers them automatically as the traces of a workhorse.

The confused representational content of the imaginative ideas can arise not only because of the way in which the imaginative process represents causal processes, but also due to the limited capacity of memory. Generally, the human body’s ability to form images at the same time (simul) limits the human mind’s ability to remember single episodes and to imagine individuals distinctly (E2p40s1, ii/121/3–5). Now, when the maximum number of distinct images in the brain is exceeded, the images get confused, memories become blurred: since the human mind cannot remember individuals separately, it employs a shortcut and the mind forms universal notions. In these notions, a number of individuals, which the subject has encountered during her life, are imagined together (simul): in this imagination, only the common features of the individuals are represented distinctly; their peculiarities are not recognizable for the cognizing subject anymore (E2p40s1, ii/121/14–20). Since the subject forms universal notions based on his encounters with particular individuals, different people with different biographies build different universal notions. This can lead to the formation of biases and prejudices: if, for example, someone has only encountered European sheep, she mistakenly represents sheep as long-tailed animals, although Moroccan sheep are short-tailed (KV2.3, i/56).

Imagination is indispensable for the knowledge of external bodies. In 2p26, Spinoza explicitly states that the human mind represents external bodies as actually existing only in imagination. This is also the reason why Spinoza regards imagination as one type of knowledge later on in his classification. But there remains an interpretive problem with respect to this issue: are, on Spinoza’s view, all imaginations inadequate, and if so, does this entail that they are false? On the one hand, Spinoza clearly states that imaginations are inadequate: “Insofar as the human mind imagines an external body, it does not have adequate knowledge of it” (E2p26c), and he also makes it clear that the first kind of knowledge, which is also named “opinion or imagination” (E2p40s2, ii/122/10–11), is the “only cause of falsity, whereas knowledge of the second and third kind is necessarily true” (E2p41). In E4p1, on the other hand, Spinoza points out that when an error regarding a particular object is removed from a false idea, the imagination or perception of the object remains the same. Therefore, “when the rays of the sun, falling on the surface of the water, are reflected to our eyes, we imagine it [i.e., the sun] as if it were in the water, even if we know its true place” (E4p1s). This shows that imagination is an ambiguous epistemic category: being knowledge, imaginations always contain some truth, but it derives from experiences that are likely to cause confusion or invite misinterpretations.

Spinoza’s ambivalence toward the epistemic benefit and danger of imagination is illustrated by his example of the winged horse. The example involves

How this example is to be construed is a matter of scholarly controversy. If we only consider the description of the child’s mental state as quoted, what Spinoza suggests is that imagining the winged horse involves affirmation of the existence of the winged horse, which is why we err unless prevented by contrary ideas. Yet, Spinoza continues by discussing the example in the following way: “Next, I grant that no one is deceived insofar as he perceives, i.e., I grant that the imaginations of the mind, considered in themselves, involve no error (2p17s)” (E2p49cs, ii/134). This description, by contrast to what is suggested in the previous quote, seems to indicate that having an imagination of the winged horse as such need not involve affirmation of its existence. Does imagination now involve affirmation or not? There is no consensus about this point in Spinoza scholarship, although Spinoza concludes his considerations of the case by explicitly denying that “man affirms nothing insofar as he perceives. For what is perceiving a winged horse other than affirming wings of a horse?” (E2p49cs, ii/134). Thus, perceiving and imagining always entail affirmation, whereas what precisely is affirmed and on what grounds gives rise to controversies.

Imagination also plays a significant practical role in the Ethics: it is the source of certain conceptions arguably indispensable for the human outlook on the world. Among these are, for instance, plurality, becoming, the use of signs, and the perception of singular things (E1p15s, ii/59); it is also through imagination that we cognize objects as past and future, or as contingent (E2p44c1, ii/125–26). Imagination also gives rise to consideration of things as final causes, for instance, when a house is considered to be suitable for habitation by imagining it to fulfill the subject’s desire for habitation (E4pref, ii/207). In a similar way, imagination evaluates things upon their usefulness and the pleasure they provide. As a result, people call things “good, evil, order, confusion, warm, cold, beauty, ugliness” (E1app, ii/81): the subject frames these concepts when she evaluates objects based on how they contribute to her well-being. This means that these terms do not indicate the properties of objects, but rather the way in which the subject’s body is affected by them. Spinoza adopts an appraisal-relativist account of value terms: since the quality of affections depends on the nature both of the affecting body and of the affected body, music can be healthy for one person and unhealthy for the other, depending on their individual constitution (E4pref, ii/208). This is why value judgments, if they are based on imagined qualities, do not reliably guide us to achieve happiness in life. For the same reason, imaginations hardly lead to agreement between people of different cultures and characters: whereas people in similar situations tend to have similar imaginations and personal experiences, cultural differences amount to different imaginations and memories. This shows how the same mechanism based on the imagination that allows for cooperation and community-building between people who share culture, character, and temperament, also explains why people of different cultures, professions, or historical backgrounds, when they merely rely on the imagination, tend to disagree with respect to all sorts of things.

As ideas through which the human mind can cognize purposes, imaginations are arguably also relevant for morality insofar as they provide motivations for actions: “the mind, as far as it can, strives to imagine those things that increase or aid the body’s power of acting” (E3p12). Spinoza describes an increase in the body’s power of acting as joy, a decrease as sadness. Therefore, “We strive to further the occurrence of whatever we imagine will lead to joy, and to avert or destroy what we imagine is contrary to it, or [sive] will lead to sadness” (E3p28). That is, human motivation can stem from what humans imagine to have an impact on their power of acting. And what they imagine to have such an impact need not reflect what is the case: as we saw above, the imaginations of a person indicate the state of her body rather than the nature of the external body. Also, since, as we have also already noted, imaginations follow the order of affections rather than the order of things, “[a]ny thing can be the accidental cause of joy, sadness, or desire” (E3p15). All this suggests that affects brought about by accidental causes can motivate irrational belief and action (E3p46).

Establishing associations between ideas and, thereby, also between images in memory, the imagination can also have positive use in regulating people’s life. This is, for instance, the case when certain maxims of life, whether they are originally formed as propositions in people’s minds or merely suggested by some association, are embodied as habits or character traits. For example, if a subject associates the imagination of certain wrongs with the notion of generosity, she is less prone to avenge the wrongs done to her, because whenever she is wronged, she is also reminded of the virtue of generosity and will thus consider the wrong as something to be countered by love rather than by hate. These maxims of life, however, are not always entirely successful; sometimes they rely on associations that just are too weak in comparison with the power of external causes. But even then, such maxims will have an effect: if one is wronged gravely, one becomes less angry if one has memorized the maxim to counter one’s being wronged with love or generosity (E5p10s, ii/287–88).

Whether or not the imagination plays a role in our well-being also depends on how much influence other sources of cognition may be granted. The ultimate human good, for example, is the intellectual love of God, achieved by intuitive knowledge of God. Constituted by adequate and complete knowledge of things, this good is such that it cannot be defeated by external causes; but to achieve it, the impact of imagination on cognition must be diminished (E5p39s). In politics, by contrast, which is a sphere of human activity necessitated and characterized by the lack of certain knowledge, imaginative processes play an important and often productive role. This is not to deny that even in politics, intellect and reason may have a considerable impact, depending on the mentality of people in influential positions. It is in this context that in the TTP, in the chapter on the prophets, intellect and imagination are rival mental capacities to the effect that people who have powerful imagination are less able to use their intellect, whereas those who can grasp many things with their intellect are less able to imagine things (iii/29). Spinoza in this chapter presents the intellect as epistemically preferable to imagination, but he does not preclude that in situations where certain knowledge is practically unavailable, the imagination may be useful, for example, to persuade people of something that is eventually good for them. This is also what allows us to make sense of Scripture despite its telling imaginative stories as if they were history: Scripture’s “concern is not to convince people’s reason, but to affect and fill their fantasy and imagination” (iii/91), and it teaches by experience rather than by proofs (iii/167). Because Scripture is aimed to have an impact on imagination rather than the intellect, it can positively influence the behavior of those who are not able to follow scientific proofs or in situations where certain knowledge is not available.

Imitation of AFFECTS (imitatio affectum) is a law of human nature for Spinoza. It is a fundamental principle of affective life and inter-individual exchanges, based on imagining a thing that is like us. Spinoza defines the imitation of affects in E3p27: “If we imagine a thing like us, towards which we have no affect, to be affected with some affect, we are thereby affected with a like affect.” This proposition does not explain how we can share (or not) the affects of those we love or hate, but how we can imitate the affects of those toward whom we have no affect. It obeys a logic of similarity. How does it happen?

This mechanism of imitation of affects is grounded in the nature of “images,” that is, affections of the human body whose ideas represent external things as present (E2p17s3). If the nature of external body is like the nature of our body, then the imaginative idea that we form of the external body’s affection involves a similar affection of our body. While imagining someone like us to be affected with a feeling, we will experience therefore the like affect. Spinoza gives an illustration of this process in his account of emulation (aemulatio) in E3def33exp: “If someone flees because he sees others flee, or is timid because he sees the others timid, or, because he sees that someone else has burned his hand, withdraws his own hand and moves his body as if his hand were burned, we shall say that he imitates the other’s affect.”

The imitation of affects, as we can see, seems to be a reflex and does not necessarily involve reflection. It can be automatic and occur involuntarily without judgment. It requires the perception of the other’s affect, but it does not perforce include that one understand the nature of the affect, or have felt it previously. The case of children in E3p32s is very instructive in this regard. “For we find from experience, that children, because their bodies are continually, as it were, in a state of equilibrium, laugh or cry because they see others laugh or cry. Moreover, whatever they see others do, they immediately desire to imitate it.” Children’s behavior shows that imitation of affects is not grounded in a mental process of association of ideas on the basis of previous experience. Children cry and imitate sadness, because they see someone crying and they observe his behavior. The imitation is spontaneous and involves neither an interpretation of the situation nor a previous experience or memories, establishing an association between the feeling of sadness and the present behavior. Children may imitate affects that they have never experienced before. But is what Spinoza has in mind here indeed only a corporeal process similar to what we call “mirror neurons” nowadays?

Actually, in Spinoza, imitation of affects is not always spontaneous and thoughtless. The principle of association of ideas can certainly play a part and reinforce its power. In the past, when I was sad or glad, I behaved in a certain kind of way and I may have been aware of such behavior. I have thus established an association between a certain kind of behavior and the affect of sadness or joy. When I observe such behavior in something like me, I associate it with the state of sadness or joy and then I am determined to feel such affects. However, the imitation of affects is not necessarily linked with memory and previous experiences.

The main interpretative problem is to know whether for Spinoza imitation of affects is due to a real similarity of bodies or whether it depends on fictional representation of a thing like us. In fact, both interpretations are possible. I can imitate someone else’s affects because our bodies “agree” in certain things. They not only have common properties (see E2p38–39), but they can even agree “in nature” (see, e.g., E4p31–35). In this case, my “image” of something like me, will include a state of my body very similar to his state and will be adequate in me.

But for Spinoza I can imitate the affects of a thing which is not really like me, too. Adam’s imitation of animals is one of the most famous examples of that kind of imitation, based on the fiction of a similarity. According to the story of the first man related by Moses, Spinoza says, postlapsarian Adam believed the animals to be like himself and this confusion led him to imitate their affects:

Thus, imitation of affects can be a form of what Spinoza calls “bondage,” that is, a “lack of power to moderate and restrain the affects” (E4pref), especially when we reproduce the behavior of animals or ignorant human beings with whom we do not agree in nature. But in itself imitation is not good or bad; it is amoral in nature. This is one of the reasons why Spinoza distinguishes imitation and emulation in E3def33: “it has come about by usage that we call emulous only one who imitates what we judge to be honorable, useful or pleasant.” The basis for that distinction between imitation and emulation is not the fact that emulation has one cause and imitation another. It is not a difference of cause, but a difference of value that involves a judgment and a desire. For Spinoza, emulation is a kind of imitation of the affects related to desire. Emulation is “the desire for a thing which is generated in us from the fact that we imagine others like us to have the same desire” (E3p27s). Generally speaking, imitation of affects is ambivalent. It increases the power of sad or joyful passions by a form of contagion and it rules the inter-individual life and social exchanges for better or worse.

Imitation has a key role in ethics and politics. This is made clear in TP:

Civil society and the commonwealth as Spinoza understands them do not rely primarily on an agreement brought about by reason but on a common affect. Reason is here powerless indeed. So imitation of affects can help produce common affects and reinforce the union. But, again, it can both unite and divide people and it is often harmful too.

Immediately after the definition in E3p27, Spinoza deduces the forms of imitation of affects, such as pity and ambition, that play a great part in society and can be in turn sources of harmony or tyranny. The first one, pity, is related to sadness, the second one, ambition, to joy. “This imitation of the affects, when it is related to sadness is called pity” (E3p27s). Pity is a sadness arisen from injury to another: it can be helpful, despite its passive nature that diminishes our power of acting, because it determines us to free the thing we pity from its suffering. Ambition is the striving to do (or to omit doing) whatever we imagine others to look on with joy. Despite its joyful nature, this affect is morally ambivalent. Ambition is “an excessive desire for esteem” (E3DA44). It leads us to imitate the vile passions of the people to seduce and be approved and often becomes a striving to bring it about that everyone approve one’s love or hate, or general way of living. Imitations of affects can be thus a poisoned gift to those who confound apparent similarity and real agreement.

Responding to henry Oldenburg’s request to clarify his views about the relation between God and Nature (Ep71), Spinoza writes: “I favor an opinion concerning God and Nature far different from the one Modern Christians usually defend. For I maintain that God is, as they say, the immanent, but not the transitive, cause of all things” (Ep73, iv/307). In the Ethics, Spinoza does not define the notion of causa immanens, but we can easily retrieve the precise meaning of the term by scrutinizing E1p18d in which Spinoza proves that “God is the immanent, not the transitive, cause of all things [Deus est omnium rerum causa immanens; non vero transiens].” The proof relies on two claims Spinoza established earlier in the Ethics: that all things are “in” God (E1p15), and that God is the “efficient cause” of all things (E1p16c1). Thus, an immanent cause is an efficient cause whose effect is in the cause, while a causa transiens is an efficient cause whose effect is not in the cause. (In the secondary literature, the relation of being-in is commonly referred to as ‘inherence’; notably, Spinoza himself uses the terminology of “inherence” only once, Ep12, iv/61.) The same distinction also appears in KV, where Spinoza discusses God’s causation in the context of a taxonomy between the various kinds of efficient causation. The second division in this taxonomy reads: “God is an immanent cause and not a transitive cause, since he does [werkt] everything in himself, and not outside himself” (KV1.3, i/35). The terminology of “external”/“internal” cause seems to denote the very same distinction (see KV2.26, i/110). In HG, Spinoza suggests that the Hebrew verbal structure התפעל (hitpael) signifies immanent causation (HG12, i/342/22).

In some popular literature – e.g., in the exchanges surrounding the Pantheismusstreit of the 1780s – Spinoza’s God was said to be ‘in the world.’ This understanding of the relation denoted by ‘in’ is different from, and in fact opposite to, Spinoza’s use of the term. For Spinoza, the in-another relation is one of a certain asymmetric ontological and conceptual dependence (what is in another cannot be and be conceived without the other). Thus, Spinoza argues that all things are (or, if you wish, the world, qua the totality of all finite things, is) in God, but he never claims that God is in the world, or in all things, insofar as God is not dependent on the totality of finite things.

Spinoza was fully aware of the fact that his view of God as “inseparable” from nature (see Ep6, iv/36 and Ep73, iv/307) was opposed to the beliefs of his Christian contemporaries. Nevertheless, he suggested that within both Judaism and Christianity there are anticipations of his view:

Spinoza’s mention of corrupted ancient Hebrew traditions here is plausibly a reference to the Kabbalah (which literally means tradition and was widely considered as corrupted ancient wisdom), within which panentheistic views – i.e., views which assert that the world is in God, but does not exhaust God – were extremely common.

There are two texts that are crucial for Spinoza’s account of an “individual” (individuus), both of which focus on the case of bodily individuals. The first of these is a 1665 letter to the Secretary of the Royal Society, Henry Oldenburg, in which Spinoza responds to the request of his correspondent that he address “that difficult question concerning our knowledge of how each part of Nature agrees with its whole and in what way it agrees with other things” (Ep31). In response, Spinoza claims that since “all bodies are surrounded by others, and are determined by one another to existing and producing an effect in a fixed and determinate way, the same ratio of motion to rest [eadem rationem motus ad quietam] always being preserved in all of them at once,” it follows that “every body, insofar as it exists modified in a definite way, must be considered as a part of the whole universe, must agree with its whole and must cohere with the remaining bodies” (Ep32).

The view in the letter to Oldenburg is picked up and developed in our second crucial text, an extended aside on the nature of bodies that follows the suggestion in the scholium to E2p13 that the human body is no different from other “individuals.” In this section – labeled in the literature as the ‘Physical Digression’ (Lachterman Reference Lachterman1977; also the ‘Short Physical Treatise’ in Garber Reference Garber1994; and the ‘Physical Interlude’ in Peterman Reference Peterman and Melamed2017) – Spinoza stipulates that physical individuals are bodies composed of parts that are compelled by surrounding bodies to remain in contact in such a manner that they “communicate their motions in a certain fixed manner [ratione]” (E2p13; E2def[8]; ii/99–100). The view here – familiar from the letter to Oldenburg – is that such individuals have a particular “nature” or “form” reflected in a “union” of internal parts that yields a specific “ratio of motion and rest [motus et quietis rationem]” among those parts (E2p13, E2L4d) (on this account of individuation, see Garrett Reference Garrett, Barber and Gracia1994). Moreover, Spinoza’s claim to Oldenburg that the bodies are “part of the whole universe” is reflected in his view in the Physical Digression that finite bodily individuals themselves compose further bodily individuals, and that “if we proceed in this way to infinity, we will easily conceive the whole of nature to be one Individual, whose parts, that is, all bodies, vary in infinite ways, without any change of the whole Individual” (E2p13s, E2L7s).

The indication in the Physical Digression seems to be that the whole of the universe is an individual in the same sense that the finite bodily individuals that compose it are. However, this result is not entirely unproblematic. For instance, in the Physical Digression Spinoza identifies bodies as “singular things” (E2p13s, E2L3d), and he earlier defined singular things as “things that are finite and have a determinate existence” (E2def7). In order to claim that the infinite universe as a whole is itself a body (which seems difficult for him to deny), Spinoza must hold either that some bodies are not singular things or that some singular things are infinite.

Another question concerns the ontological status of “the whole of the universe” as an infinite individual. The mere fact that this individual is composed of parts rules out its identification with extended substance, given Spinoza’s insistence in the Ethics that both substance and its attributes are completely indivisible, and so cannot be composed of parts (E1p12–13). Moreover, there is the claim in his earlier KV, that “division never occurs in the substance, but always and only in the modes of the substance” (KV1.2). Thus, it would seem that the divisible infinite individual is to be identified with some mode of extended substance. In fact, in E1p21–23 Spinoza introduces the notion of an “infinite mode,” distinguishing there between an infinite mode that follows immediately from the “absolute nature of an attribute,” on the one hand, and an infinite mode that follows from an attribute insofar as that attribute is modified by an infinite mode, on the other. As an example of the first kind of mode in the attribute of Extension, Spinoza offers in the Ethics “motion and rest [motus et quies]” (E1p32c2; cf. KV2.19). This text provides no example of the second kind of mode in extension, but when pressed by his perceptive critic Ehrenfried Walther von Tschirnhaus in correspondence, Spinoza offers “the face of the whole Universe [facies totius Universi], which, although varying in infinite ways, yet remains always the same,” referring his correspondent to the discussion in the Physical Digression (Ep64). It would seem, then, that we are to conceive of the infinite individual composed of all finite bodily individuals as itself an infinite modification of the infinite mode of motion and rest (see Schmaltz Reference Schmaltz1997). We have an alternative here to the view – prominent in the literature – that the infinite modes of Extension are to be identified with the laws of nature that govern the material universe (for a source of this view, see Curley Reference Curley1969).

According to Spinoza, there are in God ideas of everything that follows from his essence (E2p3). One consequence here is that there are ideas of all finite bodily individuals that constitute the material infinite individual. Given Spinoza’s suggestion that the mind associated with a body is simply the idea of that body (E2p11), these ideas serve as the minds of those individuals. It would seem that there also must be a mind that consists in an idea of the material infinite individual. However, Spinoza is somewhat unclear about the nature of the mental infinite individual. In the older literature on Spinoza (see, e.g., Joachim Reference Joachim1901), this individual is typically identified with the “infinite intellect of God” – alternatively the infinite “idea of God” – that comprises all human minds (E5p40s; Ep32). Yet Spinoza himself indicates that this infinite intellect or idea is in fact an immediate infinite mode of Thought, and thus something that corresponds to motion and rest, the immediate infinite mode of Extension (E1p21d; cf. KV1.9). The question remains of what could constitute the mediate infinite mode of Thought that corresponds to the infinite individual that serves as the infinite modification of this mode of Extension. One answer that draws on Spinoza’s discussion in Part 5 of the Ethics is that the mediate infinite mode of Thought is to be identified with the “infinite Love of God” that has the infinite idea of God as its cause (E5p36d,c). What is still unclear, though, is precisely how such an answer could be brought into line with the account of the material infinite individual provided in the Physical Digression (see, again, Schmaltz Reference Schmaltz1997).

One of Spinoza’s many unorthodox theological moves is to banish the intellect from the divine essence. Unlike most of his predecessors, for whom God’s intellect is identical to God’s essence, Spinoza takes God’s “infinite intellect [intellectus … infinitus]” to be only a modification (“mode”) of divine Thought, so only an effect understandable through God’s essence, rather than a part or an aspect of that essence itself (E1p31–33).

Within Spinoza’s metaphysical scheme, the infinite intellect is typically classified not just as a mode but, more specifically, as an “immediate infinite mode” – that is, a mode that follows directly from the “absolute” nature of an attribute (that is, presumably, from the unmodified attribute, E1p23, though see Schmaltz Reference Schmaltz1997). Already in the early KV, Spinoza offers “Intellect in the thinking thing,” alongside “Motion in matter,” as an example of “etern[al],” “immutable,” and “universal Natura naturata” (produced nature) “immediately depend[ent]” on God (KV1.9).

Intellection as such is something “we perceive as clearly as possible”; indeed “we can understand nothing that does not lead to more perfect knowledge of intellection” (E1p31s). This suggests that intellection is intrinsically reflexive: in understanding anything whatsoever, we understand not only the object represented, but also the act of understanding itself (cf. E2p21s).

Unlike “imagination,” “intellect” is thinking that traffics only in true ideas (e.g., E1p30d). Hence, Spinoza writes that the infinite intellect’s “sole property is to understand everything clearly and distinctly at all times” (KV1.9[3]). This also suggests that to Spinoza “intellect” means something closer to acts of understanding (intelligere), rather than a certain body of knowledge, or a “faculty” (cf. E1p31s, E2p48s; Wolfson Reference Wolfson1934, 1.238–39). Human “intellects” – that is, human “minds [mentes]” insofar as they genuinely understand – are “parts” of this eternal divine intellect: all together they “constitute” the infinite intellect (E2p11c, E5p40s; cf. Joachim Reference Joachim1901, 96).

In his demonstrations Spinoza often appeals to what an “intellect,” or an “infinite intellect,” understands (e.g., E1def4, E1p16). However, it’s not obvious whether to understand these references as (1) references to the intellect as a mode; or (2) a generic appeal to a certain norm of genuine understanding, which grasps things as they really are; or finally as (3) references to properties specific to intellectual Thought as opposed to imaginative Thought.

Here is an example of this interpretative quandary. E1p16 appeals to what “can fall under an infinite intellect” to license a conclusion about what actually comes into being (namely, all that can be “inferred” by “intellect” from the essence of something “absolutely infinite”). If we understand E1p16’s references to “intellect” as references to the concrete mode, this would imply that this mode is explanatorily prior to all modes (including itself). Such a reading renders E1p16 viciously circular (since it explains the existence of the infinite intellect by appeal to that intellect). Accordingly, it seems preferable to read Spinoza’s references to “intellect” in E1p16 not as references to the specific mode, but rather as making the general point that God intelligibly produces everything conceivable given divine nature, and that, properly understood, the relevant causal relations are governed by the same conceptual necessity as inferences (cf. E2p3s; Bennett Reference Bennett1984, 77, 122–23).

Perhaps the longest-running interpretative controversy involving the infinite intellect concerns its relation to what Spinoza calls the “infinite idea of God [Dei infinita idea]” (E2p8d). Let us first say a few words about this idea itself.

Idea Dei is the idea “[i]n God … both of his essence and of everything that necessarily follows from his essence” (E2p3) – presumably, the idea of all essences and existents alike (cf. E1p25s). Although idea Dei is just a mode, it has some very distinctive properties. For one, as a true idea of an infinite substance, it has, like Descartes’s idea of God in Meditation 3, an infinite objective reality. Second, within the global “parallelism” of things and ideas (E2p7), it plays, with respect to the production of ideas, a causal role isomorphic to the role of substance itself with respect to the production of things: “whatever follows formally from God’s infinite nature follows objectively in God from his idea in the same order and with the same connection” (E2p7c; emphasis added). This brings Spinoza’s metaphysics of Thought close to the Neoplatonist picture, on which God’s intellect is the second most fundamental entity after divine essence, although of course Spinoza wouldn’t follow Neoplatonists in holding that things under all attributes causally depend on the intellect (the seeming counter-indication at E1p17s[ii] is part of a dialectical argument whose premises Spinoza doesn’t endorse).

How should we understand the relation between this infinite “idea” and the infinite “intellect”? The majority consensus is that these are just two different names for the same mode of Thought (Giancotti Reference Giancotti and Yovel1991; Gueroult Reference Gueroult1968, 314–20; Melamed 2013, 133; Schmaltz Reference Schmaltz1997; Wilson Reference Wilson and Wilson1999b; Wolfson Reference Wolfson1934, 1.239–41). There is some indirect textual evidence for this conclusion: Spinoza describes both the idea and the intellect as “immediate” modes (KV1.9; KVApp2[4–5]; Ep64); as comprehending “essences” (E5p40s, KVApp2[3–4]); and identifies each separately with Christ (E4p68s, KV1.9[3]) (arguably in order to naturalize a religious trope – so Giancotti Reference Giancotti and Yovel1991). Identifying the infinite intellect and the infinite idea would also be consistent with Spinoza’s reduction of “minds” to more or less complex ideas (E2p15, E2p48s). If the infinite intellect is, like a finite mind, just a bundle of ideas, then we have good reason to think of it as an infinite “idea.”

One could however take the infinite intellect and infinite idea to be two different modes (e.g., Hallett Reference Hallett1957, 31–32), perhaps the immediate and mediate infinite modes of Thought respectively. On such a reading, the infinite idea would be an effect of the infinite intellect, in line with traditional conceptions of intellect as productive of and distinct from its ideas. Partisans of this two-modes reading often appeal to the list of infinite modes Spinoza gives in Ep64, following Tschirnhaus’s demand via Schuller (presumably made in response to E1p21–23) for examples of “those things which are produced immediately by God” and of “those which are produced by some infinite mediating [mediante] modification” (Ep63). Spinoza replies, “examples of the first kind are, in Thought, absolutely infinite intellect, and in Extension, motion and rest; an example of the second kind is the face of the whole Universe” (Ep64, iv/278). This reply is often read as offering two examples of extended infinite modes (motion and rest, and the “face of the whole universe,” as immediate and mediate modes of extension respectively), but only one example of an infinite mode of Thought (the “absolutely infinite intellect” as the immediate mode). This reading leads some commentators to try to fill in the perceived gap in Spinoza’s list, by proposing that the “infinite idea of God” is the ‘missing’ mediate mode of Thought.

But there are other ways to interpret Spinoza’s list. The “face of the whole universe” could name the mediate infinite mode under both attributes – whether (as Wolfson Reference Wolfson1934, 1.247 has it) because this “face” identifies the causal order common to all attributes or (as Giancotti Reference Giancotti and Yovel1991 and Joachim Reference Joachim1901, 95 propose), because the changing material “face” of the universe – bodies coming into and out of existence – also specifies the fundamental contents of all human ideas (cf. E2p13). Alternatively, following Gueroult (Reference Gueroult1968, 318), we could distinguish between (1) the infinite idea/intellect as the immediate infinite mode of Thought and the collection of ideas of essences, and (2) the mediate infinite mode of Thought as a collection of ideas of temporal existents (i.e., of ideas of the changing “face of the universe”) and an infinite “will” composed of finite strivings. (Spinoza defines “will” as striving considered under the attribute of Thought [E3p9s].)

Spinoza’s mention in Ep64 (and only there) of an “absolutely” infinite intellect also generates the question of how, if at all, this intellect differs from the “infinite intellect” of the Ethics. Most commentators deny any significant difference (Wolfson Reference Wolfson1934, 1.240–41; Schmaltz Reference Schmaltz1997; Melamed Reference Melamed2013b, 182).

If infinite intellect and infinite idea are one and the same mode, why does Spinoza refer to it by two different names? Here is one possible explanation. According to Spinoza, we can think of any idea merely as an act of thinking or as having a particular representational content. To think of an idea in the first way is to consider its “formal” reality. To think of it in the second way is to consider its “objective” reality. Given this distinction, and given that “intellect” traditionally designates the thinking subject rather than the object being thought, it seems plausible that “infinite intellect” refers to the formal reality of the immediate infinite mode of Thought, while “God’s idea” refers to its objective reality. This way of distinguishing between “infinite intellect” and idea Dei seems to be confirmed by the ways Spinoza describes their respective relations to eternal ideas of bodily essences: “ideas of … modes that do not exist must be comprehended in God’s infinite idea” (E2p8); “our mind, insofar as it understands, is an eternal mode of thinking, which is determined by another eternal mode of thinking … and so on, to infinity; so that together, they all constitute God’s eternal and infinite intellect” (E5p40s). The former passage seems to emphasize thinkable content; the latter, the activity of thinking. (See Wolfson Reference Wolfson1934, 1.239–40 for a different aspectual reading.)

For most philosophers working in seventeenth-century Europe, modes are impermanent and changeable qualities or features; this is why Descartes for example insists that God has no modes (Comments on a Certain Broadsheet, AT8B.348; cf. Principles i.56, AT8A.26). Spinoza, however, departs from this consensus view of modes, introducing into his system modes that are infinite, eternal, and immutable: the so-called “infinite modes.”

It is clear that as modes, the infinite modes ontologically depend on substance, since modes only exist in virtue of being in, and immanently caused by, the one and only substance (E1p15, E1p18). It is also clear that the infinite modes depend on substance for their conceivability: modes are conceived through their substance (E1p15). But there is a lot that is unclear about these novel entities, since the texts discussing the infinite modes are few and none are straightforward.

In the KV, Spinoza briefly discusses “universal Natura naturata,” which are “eternal” and “immutable” modes immediately depending on God (KV1.9), but the fullest explicit treatment of infinite and eternal modes is found in E1p21–23. The first proposition in this cluster establishes that all things following from the “absolute nature of any of God’s attributes” – i.e., from infinite and eternal substance, insofar as it is not already modified – are infinite and eternal. The long and very obscure demonstration of this claim consists of two reductio ad absurdum arguments, the first establishing the infinity of what follows and the second establishing eternality.

Both sub-arguments begin with the assumption that there is a limited mode (call it m), “for example, the idea of God in thought [idea Dei in cogitatione],” that follows from God’s nature alone: in the first case, the mode is limited in reality, that is, it is finite rather than infinite, and in the second case, the mode is limited in duration, and so is non-eternal. On some reconstructions of the arguments, the sub-arguments have the same basic structure: for m to be limited (either so that it is finite or so that it is non-eternal), we must assume that there is another mode, n, that is limiting m. But then m does not follow from God’s nature alone, and this is contrary to hypothesis (see, e.g., Schmaltz Reference Schmaltz1997).

It is also possible to read the sub-arguments as having a slightly more complicated structure (Primus Reference Primus2019). In the first sub-argument, we suppose for reductio that there is God conceived under the attribute of Thought and a finite mode necessarily immanently caused by that substance (the idea of God in Thought). To be finite, the idea needs to be limited by something else that is also conceived under the attribute of Thought (E1def2). One potential limiter is the thinking substance in which the finite mode inheres, but to suppose that substance causes the limitation is, in effect, just to restate what has already been assumed for reductio. So, what limits the mode must be something conceived under the attribute of Thought, but which is neither the finite mode itself (since the mode cannot limit itself) nor the substance in which that mode inheres. However, to assume that there is such an external limiter amounts to positing another necessarily existing thinking substance (E1p11). In short, we have ended up supposing that there is a thinking substance that necessarily immanently causes the finite mode and another thinking substance that does not. This is absurd, however, as there is just one thinking substance (see E1p5): the one thinking substance cannot at once both cause the mode and not cause the mode. The demonstration generalizes to other attributes, so we can thus conclude that only a non-finite (i.e., infinite) mode, or what does not require such limitation, immediately follows from infinite substance.

In the second sub-argument, we suppose that there is a mode that follows with necessity from the attribute of Thought yet only endures for some time. If the mode follows with necessity from the attribute of Thought, then for that mode to not exist at certain times, we must suppose that the attribute of Thought, that is, God’s nature, is different at those times. However, to suppose that God’s immutable nature changes is absurd (E1p20c2). Again, the demonstration generalizes to other attributes, and so we can conclude that what immediately follows with necessity from the nature of substance is eternal.

In E1p22, Spinoza argues that whatever follows from a mode which “exists necessarily and is infinite must also exist necessarily and be infinite.” Spinoza says that the demonstration of E1p22 “proceeds in the same way” as E1p21d. Spinoza does not spell out the reasoning, but the demonstration presumably proceeds in two stages. In the first stage, we can assume that something finite follows from an infinite mode. The infinite mode, however, cannot be the source of this finitude, since something that is infinite can neither limit nor be limited by anything. For the infinite mode to ensure the finitude of what follows, we must suppose that the infinite mode is also finite, which is absurd. For the second stage, note that Spinoza is treating modes’ existing necessarily and their being eternal (cf. E1p10s, E2p44c2, and E1p23d). Only substance exists necessarily, or is eternal, by its own nature alone (E1def8, E1p19d). We assume that a non-necessary (non-eternal) thing follows from a necessary (eternal) mode. However, as in E1p21d, this assumption requires supposing that a necessary, eternal – immutable – nature can change, which is absurd.

E1p23 establishes, by more perspicuous reasoning, that whatever is infinite and exists necessarily (i.e., is eternal) must be a mode of God that has followed either immediately from the “absolute nature of some attribute of God” (E1p21) or mediately from God’s nature via an infinite, necessary (eternal) mode (E1p22).

Schuller asked Spinoza to provide examples of first, “those things immediately produced by God,” or the sorts of modes discussed in E1p21, and second, “those things produced by the mediation of some infinite modification,” of the sorts of modes discussed in E1p22 (Ep63). In reply, Spinoza offers as examples of the first kind “absolutely infinite intellect” in Thought and “motion and rest” in Extension (Ep64; cf. KV1.9, KV1.3, KV2.26). For an example of the second kind, Spinoza offers the “face of the whole Universe [facies totius Universi], which, although varying in infinite ways, remains however always the same,” and points Schuller to the scholium to lemma 7 following E2p13s, which says that the whole of nature can be conceived as “one individual, whose parts, that is, all bodies, vary in infinite ways, without any change of the whole individual” (ii/102).

A first question is why, in his response to Schuller, Spinoza seems to only give an example of a mediate infinite mode of Extension (see Schmaltz Reference Schmaltz1997). What would a mediate infinite mode of Thought be? More generally, what else might be an infinite mode? Infinite modes might include “formal essences” (E2p8) and universal features described by laws of nature (see, e.g., Garrett Reference Garrett and Koistinen2009), what is represented by the adequate ideas discussed in E2p38–39 (see, e.g., Curley Reference Curley1969, 57–58, Nadler Reference Nadler2006, 175, and Marshall 2008a, 63), and the entire causal series of finite things discussed in E1p28 (see, e.g., Garrett Reference Garrett and Yovel1991 and Melamed Reference Melamed2013b, 132). In Part 5 of the Ethics, Spinoza claims that the mind, insofar as it understands, is eternal, and “remains” after the destruction of the finite human body (E5p23, E5p40c). In E5p40s, Spinoza mentions E1p21 as relevant to his claim that the mind is an eternal mode of thinking. This suggests that Spinoza may hold that an eternal understanding mind is also an infinite mode.

The sense in which infinite modes are eternal is also debatable. One could argue that while these entities, as modes, depend on God for their eternal reality, they are eternal in the same sense in which God is eternal. However, there are texts suggesting otherwise. God’s existence is an “eternal truth” (E1p20c1), where this eternity “cannot be explained by duration or time, even if the duration is conceived to be without beginning or end” (E1def8, E1p19d), but the infinite modes are presented as that which “have always had to exist [semper … existere debuerunt]” – language that can be taken to mean that their eternity can be explained by duration or time (cf. E1p17s, CM1.10, KV1.9, Ep12).

A similar question concerns the sense in which infinite modes are infinite (for a discussion of different senses of infinity, see Ep12). While Spinoza insists that God’s reality is infinite in a way that is not to be conceived of as composed of parts (E1p13, E1p15s), it seems that at least some infinite modes are to be thought of mereologically: the infinite individual discussed in E2L7 is described as having parts, and the human mind is said to be “part [pars] of the infinite intellect of God” (E2p11c). It is also possible that different infinite modes are infinite in different senses. If Spinoza thinks of infinite modes along Platonist emanationist lines, he could hold that the modes “closest” to the absolute nature (those described in E1p21) are to be thought of as timelessly eternal and indivisibly infinite, while more “distant” infinite modes (those described in E1p22) are characterized by everlastingness and divisibility.

God is the cause of all things (E1p18, E1p25), and another perennial controversy regarding infinite modes is how they figure in an infinite, eternal God’s causation of finite, non-eternal things. One option is to argue that an infinite, eternal God is the cause of any finite thing only in the following sense: God causes the universal features of nature, described by laws of nature, that are necessary for the coming to be of a finite thing (Curley Reference Curley1969, 58–62 and Curley Reference Curley1988, 47–48). Another option is that God causes finite things by causing the infinite mode that is the entire causal series of finite things described in E1p28; just because a lone finite thing cannot follow from what is infinite (as is suggested by E1p21–22) does not mean that a finite thing does not follow as a part of – or perhaps as a mode of – something infinite (for an early statement of this popular view, see Garrett Reference Garrett and Yovel1991, 198). Or, finally, one could argue that all of God’s modes are indeed infinite and eternal, and that a finite, durational thing and an infinite, eternal mode are one and the same thing conceived “as actual” in different ways (cf. E5p29s); strictly speaking, it is only when a thing is conceived sub specie aeternitatis as infinite and eternal that it is a mode caused by an infinite, eternal God (Primus Reference Primus2019).

In the early modern period, the distinction between “finite” (finitus) and “infinite” (infinitus) was traditionally grounded in God’s creative power. This established a clear divide between those entities which are finite and that which is infinite. Spinoza’s notorious rejection of this metaphysical chasm via his identification of God with Nature and claim that anything that is, is in God (E1p15), met with signification opposition. Many took the very natures of being finite and infinite as necessarily incompatible, such that what is finite cannot be said to be “in” or “follow from” what is infinite. We begin by reviewing the different aspects of Spinoza’s metaphysics that he refers to as “infinite” and explain in what sense they are infinite. These include the infinity of substance, the infinite attributes, and the infinite modes. Subsequently we will review Spinoza’s answer to a possible objection in Ep12 and E1p15s. Finally we shall consider Spinoza’s characterization of finite things and interpretative routes scholars have taken in this regard.

We begin by explaining the sense in which substance is said to be infinite. A fruitful path to understanding this is to note first how Spinoza defines a finite thing in E1def2: “That thing is said to be finite in its own kind that can be limited [terminare] by another of the same nature.” That is, being finite is to be analyzed in terms of being determined, i.e., acted on by something else (of the same nature). While postponing the discussion of various issues raised by this definition, we can note what the inverse of this definition implies: being non-finite is to be analyzed in terms of being not-determined (limited), or acted on, by anything else. In E1def3, Spinoza defines a substance as “what is in itself and is conceived through itself, that is, that whose concept does not require the concept of another thing, from which it must be formed.” One, although not the sole, mark of a substance then, is its causal independence, that is, “being in itself.” Causal independence, in turn, can be analyzed negatively in terms of not-being-limited, not-being-acted on, by anything else. A substance then, is precisely the kind of thing that is non-finite, or better yet, infinite. Likewise, the conceptual independence (being “conceived through itself”) stated in the definition of substance, is also inversely mirrored in the example added to E1def2: “a body is called finite because we always conceive another that is greater.” While finite things are conceived through other things, what is infinite is not conceived through something else, that is, it is conceived through itself. The connection between “substance,” causal and conceptual independence, and “infinity” is made explicit in the first few propositions of Part 1 of the Ethics. In E1p6, Spinoza claims that no substance can be created by another substance, that is, determined by another substance. Subsequently, in E1p8, he claims that any substance is infinite, that is, not determined, acted on, or caused by another substance. Infinity, then, insofar as it attaches to the substance, is to be understood in terms of causal and conceptual independence.

To see how “infinity” is associated with attributes, we can begin by noting that in E1def6 Spinoza defines God as “a being absolutely infinite, that is, a substance consisting of an infinity of attributes, of which each one expresses an eternal and infinite essence.” We can note three iterations of “infinite” in this definition. The first is “a being absolutely infinite” which is constituted by “infinite attributes” (which is the second iteration). Attributes, by E1def4, are “what the intellect perceives of substance as constituting its essence.” Some have taken Spinoza in E1def6 to claim that “infinite attributes” means a cardinal infinity of attributes, that is, God has Attribute(1), Attribute(2), Attribute(n) … Attribute(n+1). However, Spinoza can also be understood to mean by “absolute infinity” a totality or plenum of attributes, without committing to anything with respect to the number of attributes of God. That is, on this reading, God is a being that has all the attributes – and lacks no attribute – which express eternal and infinite essence. The distinction between the two readings can be traced to an ambiguity of the Latin which reads: “Per Deum intelligo ens absolute infinitum hoc est substantiam constantem infinitis attributis quorum unumquodque æternam et infinitam essentiam exprimit.” Since there are no definite articles in Latin, the definition can be read either as holding that God is constituted by “an infinity of attributes” or as stating that God is constituted by “infinite attributes.” The second meaning and third iteration of “infinite” in E1def6 refers to the essence of substance. Each attribute, independently, is infinite in that each expresses the essence of substance, that is, as we previously saw, its conceptual and causal independence.

While Spinoza’s metaphysics is populated by some well-established ontological categories, such as substance, attribute, and modes, he further furnishes his ontology with what he calls “infinite modes.” Spinoza defines a mode in E1def5 as “the affections of a substance, or that which is in another through which it is also conceived.” This means that although an infinite mode is infinite, it can nonetheless be “in another and conceived through another.” Modes are in substance and are conceived through an attribute. The kind of infinity that attaches to these entities then is not to be understood as causal or conceptual independence. One way to understand their infinity is by their pervasiveness throughout substance. They are infinite in the sense that they lack spatio-temporal limits and are present throughout substance. Spinoza offers some examples of infinite modes in his correspondence with Schuller: these are, in Extension, “motion and rest” and “the face of the universe,” and, in Thought, “infinite intellect” (Ep64). And so, any particular thing that is extended has some degree or other of motion and rest, and so “motion and rest” is pervasive throughout Extension. The “infinite intellect” is pervasive in that, for any particular thing under the attribute of Thought, there is an idea of it in the infinite intellect.

Spinoza identifies various reasons why philosophers and mathematicians have arrived at contradictions when thinking about infinity (Ep12, also known as “The Letter on the Infinite”, and E1p15s). Spinoza is, in part, forestalling in these texts a possible objection, namely, that Extension cannot be infinite. That objection would run something along the following lines. The infinite substance is perfect and therefore cannot be composed of parts. Were it composed of parts, the parts would be both ontologically and conceptually prior to it – and so it would no longer be an infinite substance. However, Extension, by its nature, is divisible into separable parts. Therefore, the objection would go, Extension cannot be an attribute of the infinite substance. By way of diagnosing where the objection goes astray, Spinoza claims that those who hold such a view do not distinguish sufficiently between “substance” and “mode” on the one hand, and “intellectual understanding” and “imagination” on the other. When conceiving corporeal substance properly, that is, via the intellect alone, we ought to recognize that it is a substance and therefore infinite and not composed of parts, that is, causally and conceptually independent. Particular bodies are modes of substance and therefore not, strictly speaking, its component parts. While modes are divisible, they are not separable and cannot exist independently from substance and other modes. In Ep12 Spinoza explains why some might think that extension is composed of bodies: when we imagine particular bodies, we can imagine them as being distinct from one another, that is, we imagine them as if they were substances. We arrive at absurdities when we think that bodies are in fact both separable and infinitely divisible. Furthermore, the imagination allows us to consider a discrete quantity and divide it ad infinitum and then we erroneously abstract from this that the nature of Extension is such that it can be divided infinitely into discrete parts. Furthermore, these kinds of abstractions are the basis of our notions of “duration,” “quantity,” “time,” and “measure.” We erroneously think that these are infinite, but they are infinite only in that we can divide them as we like in our imagination. However, Spinoza claims, when we are careful not to rely on the imagination, we can recognize what is infinite by nature, and what is divisible indefinitely in the imagination, and can thus avoid falling into the traditional paradoxes concerning the infinite.

We turn now to discuss Spinoza’s concept of “finite.” In E1p14 Spinoza claims “Except God, no substance can be or be conceived,” and he supplements this in E1p15 by claiming that “Whatever is, is in God, and nothing can be or be conceived without God.” This entails first that finite things cannot be substances, and whatever is finite, is in substance and must be conceived through the infinite substance. This makes clear why “infinite” and “finite,” although opposites, are not dichotomous for Spinoza. Whatever is finite, is intimately linked with that which is infinite, so much so that whatever is finite cannot be conceived without conceiving it through that which is infinite. There are several senses in which finite things are infinite and conceived through what is infinite for Spinoza. First, as we just mentioned, finite things are in the infinite substance. Second, finite, or “singular” things, as Spinoza sometimes labels them, are determined by an infinity of other singular things (E1p28). Third, the actual essence of singular things, which is their striving to persevere in their being, has no limit in time (E3p8).

Although finite things are conceived through what is infinite in various ways, they are not absolutely infinite. As we saw in E1def2, the salient mark, then, of something being finite is that it is limited, or determined, by another. Being determined implies being acted on by another, that is, being in a causal (and conceptual) relation with something else. This is made clear by the example Spinoza provides in the definition itself: “a body is called finite because we always conceive another that is greater. Thus, a thought is limited by another thought. But a body is not limited by a thought nor a thought by a body” (E1def2). Causal relations, however, can only hold among things of the same nature. Spinoza proves this last point in the third proposition of Part 1: “If things have nothing in common with one another, one of them cannot be the cause of the other” (E1p3). The definition then points to three elements that constitute what it means to be a finite thing: (1) being limited, (2) having this limitation caused by something else (and therefore conceived through it), and (3) that which is causing the limitation is of the same nature as the thing being limited.

In E1p28 Spinoza further articulates how finite modes are to exist in the infinite substance. In the demonstration to this proposition, he makes an important negative point: a determinate finite mode cannot follow immediately from God’s absolute infinite nature. As he showed in an earlier proposition, whatever follows from the “absolute nature” of any of God’s attributes is infinite and eternal (E1p21). Therefore, determinate finite things, he claims in E1p28, are “determined to exist and produce an effect” by other finite things which are determined to produce an effect. These, in turn, are also determined to exist and cause an effect by other finite modes, “and so on to infinity.” Any finite mode, then, is determined by an infinity of finite modes, while also causally determining other finite modes. Opinions differ as to how to understand this infinity: some assume it is a cardinal infinity of a single or multiple parallel chains, while others read it as a totality of finite modes. A second major point of disagreement is the understanding of the nature of the necessity that attaches to finite modes, that is, how to understand Spinoza’s claim in the demonstration that finite modes do not follow immediately from God’s absolute nature. Some have taken this as evidence that, although determined, the necessity attached to finite modes is different in kind from those things that follow immediately from God’s nature, while others have argued that the nature of necessity itself is the same, even if mediated via other modes. In either case, the determination described in E1p28 anchors Spinoza’s subsequent famous claim that nothing in nature is contingent (E1p29).

There are at least two places where Spinoza associates finitude or determination with negation and non-being. In the demonstration to E1p8 Spinoza claims: “Since being finite is really, in part, a negation, and being infinite is an absolute affirmation of the existence of some nature, it follows from [1]p7 alone that every substance must be infinite.” Likewise, in Ep50 he says:

These kinds of claims have made some wonder whether, ultimately, finite things can have a real ontological standing at all for Spinoza. Among the first to raise such a concern was his friend Tschirnhaus. In Ep80, Tschirnhaus asks Spinoza how he can deduce determinate bodies from infinite Extension, seeing as there is no determination to be found in an infinite Extension. A version of this objection is echoed later on by Hegel who focuses on Spinoza’s characterization of finite things as being negations and claims that negations insofar as they are negations do not have being at all, and therefore strictly speaking cannot have being in the infinite substance (Reference Hegel, Rockmore, Haldane and Simson1995, 2.154). Both identify what appears to be an ontologically unbridgeable gap between what is infinite and what is finite, one that prevents us from understanding both how finite things follow from the infinite substance, seeing as in the infinite substance as such there is no determination or negation, and whether they can have any ontological standing at all. There is a tradition within Spinoza scholarship which gives weight to these types of concerns and by way of resolving the tension understands finite modes as being merely ideal, phenomenal, or at least thought-dependent. In these readings, the conceptual language in the definition of finite, for example, is given much attention.

Others have resisted these idealist-leaning interpretations of finite modes. One reason for resisting this route is that if finite things in general turn out to be ideal, as opposed to real, then the human mind itself, being finite, would share in this status. This in turn might be seen to be in tension with Spinoza’s characterization of the prized intuitive knowledge, which seems to concern the essences of finite things, and with the aim of the Ethics as sketched in Part Five, which concerns the mind’s beatitude and eternity. Interpreters in this camp then, face the challenge of understanding finite modes in such a way that, although they are “in part a negation” and “in another and conceived through another,” they can be intelligible, have being, and be conceived through and be seen to follow from the infinite substance. Spinoza’s metaphysics, then, modifies dramatically what is mean by “infinite,” but no less radically reconceives what it means to be finite as well.

“Being in” (esse in, inesse) figures prominently in Spinoza’s characterization of the dichotomy between substance and mode.

Modes, Spinoza says, (i) are in another whereas a substance is in itself and (ii) are conceived through another whereas a substance is conceived through itself. Further, Spinoza makes clear in the first axiom of the Ethics that the dichotomy between substance and mode exhausts reality: “All things that are, are either in themselves or in something else” (E1a1).

The phrase “things that are” is doing some work here, restricting the dichotomy to what might be called “real beings,” as opposed to “beings of reason.” (A being of reason, Spinoza explains in the CM, “is nothing but a mode of thinking, which helps us to more easily retain, explain, and imagine the things we have understood,” CM i/233; italics original; as such it is distinguished from what he terms “real being.”) The force of E1a1 is roughly, then, that things that are “external to the intellect” (E1p4d) are in themselves or in something else.

It is natural to view the relation of “being in another” as heir to the Aristotelian idea of an accident’s inhering in a substance. So understood, E1a1 would be Spinoza’s way of capturing the traditional thesis that being or reality divides into substance and accident, or, to use the terminology he, following Descartes, favors, substance and mode. And, so understood, (i) and (ii) mark two standard ways in which modes or accidents were thought to depend on the substances in which they inhere: a mode depends on its substance for both its “being” and its “logos or account.” Consider Socrates’ ruddy complexion, a paradigmatic Aristotelian accident. The ruddy complexion depends for its being on the pigmentation of Socrates’ skin and all the physiology behind that. Similarly, the logos or account (“theory” might be a good approximation, for us) of the ruddy complexion runs through an account of Socrates. That is, in order to understand the complexion, we need to draw on the theory of Socrates and his physiology.

Although this approach seems reasonable, one should be aware that, with respect to terminology, Spinoza almost never employs the Latin inhaerere (for an exception, see Ep12). Moreover, while he uses a single Latin word inesse for the relation of mode to its substance when explaining Descartes’s view (see DPP1def) – as does Descartes himself, who rarely uses inhaerere – Spinoza uses two words, esse in (being in), when presenting his own views.

If we take Spinoza’s being in as his version of Aristotelian inherence, an important question arises. Spinoza holds that all real beings are in God (E1p15), and that things besides God are in God as “in another,” that is, things besides God are modes. Spinoza seems to think, then, that Peter or Paul bears the same relation to God that the Aristotelians took Socrates’ ruddy complexion to bear to Socrates. But what sense can be made of this?

Let’s begin by narrowing the scope of our question: in what sense are bodies modes of Extension (that is, modes of God insofar as God is characterized by the attribute Extension)? A human body for Spinoza is not a freestanding entity. Rather, it is an organized, dynamic pattern (ratio) of motion and rest (see the Physical Digression in Part 2 of the Ethics) and, as such, is dependent on an (ontologically prior) plenum or Extension and its principles. It requires Extension for its being, through which it is understood. Spinoza views bodies, then, in the way one might naïvely think of the Jet Stream across North America or the Gulf Stream in the Atlantic Ocean. A motion-and-rest structure like the Jet Stream must be in the atmosphere and be understood through the atmosphere (e.g., any serious understanding of what the Jet Stream is runs through the principles of meteorology, etc.). (NB: What matters here is more the motion than the stuff that the Jet Stream is composed of, which is continually changing. To think of the Jet Stream as simply a changing collection of air masses misses something important, connected with the naturalness of viewing it as a modification of the atmosphere rather than, say, a complex changing mereological sum of various parts of the atmosphere.) In a fairly intuitive sense, then, the Jet Stream is a modification of the atmosphere, as opposed to being, say, a part of the atmosphere (or a freestanding substance in its own right). What the Jet Stream does seem to be a part of is the overall motion-and-rest configuration of the atmosphere, which itself is a modification of the atmosphere. Similarly, a ratio of motion-and-rest, for Spinoza – say, the human body – is a modification of Extension, as opposed to being a part of Extension (or a freestanding substance in its own right). What the human body is a part of is the global motion-and-rest structure of Extension, which Spinoza memorably calls the “face of the whole universe” (Ep64). This global structure is itself a modification of Extension. (It is important to Spinoza’s overall outlook here that, following his understanding of Descartes, he thinks of Extension as a whole that is prior to its parts; see E1p15, Ep12.)

If we suppose that this line of thought can be satisfactorily fleshed out, we can begin to see how physical things might be modifications of an underlying substance, and begin to attach some sense to Spinoza’s view that physical things are modes. Spinoza offers a similar theory for Thought, the only other attribute to which a human mind has direct access. God, through intuiting his essence and all that follows from it, structures or modifies the attribute of Thought (E2p3). This overarching modification of Thought is the infinite intellect of God. Although “one” (E2p4), this overarching modification is further articulated into God’s particular ideas. (Roughly, the relation of ideas to the overarching infinite intellect is similar to the relation of a body to the overarching face of the whole universe.) According to Spinoza, my mind is one of these sub-modifications. Specifically, my mind is God’s idea of my body, which we might view as God’s thinking my body. As such, it is, as Spinoza says at E2p11c, a part of the global modification, the infinite intellect of God. Finally, Spinoza seems to assume that what is the case with respect to Extension and Thought, the two attributes to which the mind has direct access, generalizes to the attributes to which our minds have no direct access.

In the Aristotelian tradition, the distinction between substance and accident is sometimes associated with a view about language, so that accidents are predicated of substances, or substances serve as the ultimate subjects of predication. While such an emphasis fits with one of Leibniz’s later characterizations of substance, it does not appear to have played a major role in either Descartes’s or Spinoza’s thinking about the relation of a mode to the substance in which it is. The word praedicare is rarely used in the Ethics (it does not occur until E2p40s1). Moreover, for Spinoza, modes are realities (i.e., among “the things that are” in E1a1), whereas the items that are most commonly associated with predication – universals – are beings of reason. A term related to “predication [gezeid]” does occur frequently in the KV, but there Spinoza usually speaks of attributes being predicated of God, not modes. It may be, for example, that when a mode (the dynamic pattern of motion and rest that is Peter’s body) is in Extension, various predications will follow, for example, God/Extension is modified Peter-wise, or human-body-wise. However, if this is so, it would seem to be a corollary to Spinoza’s basic point that a real individual like Peter’s body must be in and understood through Extension in a way analogous to the way that the Jet Stream must be in and must be understood through the atmosphere.

Thus far we have considered what it might mean for one thing (Peter’s body) to be in another thing (God/Extension). What is it for something to be in itself? One might try to characterize this relation negatively: for something to be “in itself” is for it not to require something else for it to be in. But, intuitively, it would seem that there should be something positive underneath this negative characterization: some self-sufficiency, along a certain dimension, that accounts for its not needing something else in which to be. This may be why Spinoza thinks it is better to characterize substance’s independence positively, as a matter of its being “in itself,” rather than negatively, as a matter of its “not being in anything else.” If we understand the point of being “in itself” along these lines, then it would be similar to Spinoza’s characterizing God as self-caused (and positively supplying the power or force by which God exists – see CM2.6, i/260; see also E1p7d) rather than as merely uncaused.

It has been suggested that “being in another” comes in degrees, so that, roughly, the more self-sufficient something is, the less it is in another and the more it is in itself. One passage that comes up in this context is E3p6, where Spinoza writes, “Each thing, insofar as it is in itself [quantum in se est], endeavors to persist in its own being.” Quantum in se est is a Latin idiom, which admits of different renderings. This makes it unclear how the “being in itself” in E3p6 is connected with the “being in itself” in E1def3. If one assumes Spinoza is talking about the same relation, then the qualification “insofar [quantum]” in E3p6 provides some support for the claim that Spinoza sees “being in” as admitting of respects or degrees. However, what Spinoza has in view in E3p6 is the extent to which one’s activity is sourced in one’s own essence or conatus, as opposed to being determined by other things within the causal nexus (see, e.g., E4p20s). However, whether or not one’s body acts in a way that is relatively independent of other things in one’s environment does not speak to the extent of its dependence on Extension and its principles. (After all, the fact that a storm is more powerful, and controls what happens more than other things in its environment, does not make it any less dependent for its operation on the atmosphere and its principles.) In other words, relative independence of a thing from other items in the causal nexus (what we might think of as “horizontal” independence) may not make for a relative independence of the thing from substance and its principles (what we might think of as “vertical” independence). If so, this may be a reason for keeping distinct the “being in” at issue in E3p6 from the “being in” at issue in E1def3 and E1def5.

In each of the taxonomies of cognition found throughout Spinoza’s corpus, there is a kind of cognition that is (1) inerrant (TIE[29], KV2.1) or necessarily true (E2p41), (2) a cognition of an essence (TIE[29], E2p40s2) or of the “thing itself” (KV2.2), and (3) a cognition that is intuitive in the sense that it does not require that one work through any demonstrations or practice any “art of reasoning” (KV1.1, TIE[24], E2p40s2).

Spinoza is not alone in the period in marking out a special kind of immediately self-evident cognition to be distinguished from the sort of cognition involved in going through the steps of demonstration. For example, Descartes drew a distinction between “intuition” and “deduction”: in the latter but not the former, we are “aware of a movement or a sort of sequence” in thought, and “immediate self-evidence” is only required for intuition (Rules 3, AT10.370). Certain key moves in the Meditations count as such intuitions. For example, to prove that God exists, one can just attend to the idea of God’s essence and immediately see that necessary existence belongs to God’s essence (Fifth Meditation, AT7.65); such an insight can be “just as self-evident … as the fact that the number two is even or that three is odd” (Second Replies, AT7.163–64).

In the Ethics, Spinoza identifies a kind of veridical, intuitive cognition involving essences that he calls “intuitive knowledge [scientia intuitiva].” Like the intuitive cognitions discussed in earlier works, it is an immediate insight: as immediate as recognizing that 3/6 is the same proportion as 1/2 (see E2p40s2; cf. TIE[23–24], KV2.1). But unlike the intuitive cognitions discussed in earlier works, scientia intuitiva is explicitly presented as a cognition of things proceeding from an understanding of God’s nature: it is a cognition proceeding “from an adequate idea of the formal essence of certain attributes of God to adequate cognition of the [NS: formal] essence of things.” This is an especially powerful kind of cognition: indeed, the mind’s greatest virtue is understanding things by this kind of cognition (E5p25). With scientia intuitiva, one is freed from the disruptions of affects and enjoys the greatest contentment (acquiescentia) of the mind (E5p27, E5p36s, E5p42s). One also enjoys the eternal, irrevocable “intellectual” love of God (E5p32c, E5p33, E5p37), in which human “salvation, or blessedness, or freedom” consists (E5p36s; cf. KV2.22).

As central as it is to the culminating propositions of the Ethics, it is not clear what scientia intuitiva is. One set of questions concerns the “adequate idea of the formal essence of certain attributes of God” required for the intuition. First, what are the “certain attributes”? It is plausible that since Ethics Part Two concerns the human mind, “certain attributes” means those conceivable by the human mind: Thought and Extension.

Second, what does one understand when one has an adequate idea of the “formal essence” of certain attributes? In E2p8, “formal essences” seem to refer to essences that are actual, or real, because they have eternal formal reality rather than formal reality “through which [things] are said to have duration” (E2p8c; see also E2p9, E5p29s). To have an adequate idea of the “formal essence” of something thus may mean understanding the eternal formal reality that essence has. To have an adequate idea of the formal essence of, say, Extension, is to understand Extension as enjoying the necessary, eternal, and infinite formal reality of substance, as well as to understand that there is just one extended substance (see Primus Reference Primus and Garberforthcoming for recent discussion).

A third related question is whether scientia intuitiva proceeds from such an understanding of just one attribute (like Extension), or whether it proceeds from a more complex understanding of extended substance and thinking substance as one and the same substance, God, “which is now comprehended under this attribute, now under that” (E2p7s). If one takes the first interpretive option, then one can conclude that Spinoza holds that all human minds already have the sort of understanding required for scientia intuitiva, since any human mind has an adequate idea of Thought in virtue of perceiving itself and an adequate idea of Extension in virtue of perceiving bodies (see E2p47d, E2p47s). However, it is not supposed to be easy to have scientia intuitiva (see E5p42s); if one takes the first interpretive option, one can suppose that it is difficult to proceed from this idea to the “adequate cognition of the [NS: formal] essence of things” (see, e.g., Wilson Reference Wilson1983; Garrett Reference Garrett, Sorell, Rogers and Kraye2010). If one takes the second option, however, one can suppose that the difficulty of scientia intuitiva (also) lies in coming to have the monist understanding of God (see Primus Reference Primus and Garberforthcoming for a defense of the latter option).

Another set of questions concerns the “adequate cognition of the [NS: formal] essence of things.” For example, one can ask how much complexity is grasped in this intuition. Some scholars have supposed that the cognition involves a kind of “epistemic compression” (Nadler Reference Nadler2006, 181–82): multiple discrete, ordered steps can be distinguished within the cognition, but in a sufficiently powerful mind, all these steps can be taken together at once (Garrett Reference Garrett, Sorell, Rogers and Kraye2010, 110). Again, Spinoza would not have been alone in holding such a view of intuition. Descartes also held that in some intuitions, the mind understands in one act of mind what it may have hitherto grasped via a sequence of intuitions; with practice, one can expand what can be grasped in one instantaneous act of mind (Rules 7, AT10.387–88).

One can also ask what exactly one understands about things through this (perhaps internally complex) intuition. It has been argued that in scientia intuitiva, one understands, in a single act of mind, how exactly some individual essence, or “that without which the thing can neither be nor be conceived, and which can neither be nor be conceived without the thing” (E2def2), follows from an attribute of God. Such an understanding is an apprehension of an infinity of causal details (see Wilson Reference Wilson1983, Nadler Reference Nadler2006, and Garrett Reference Garrett, Sorell, Rogers and Kraye2010). Others have emphasized that scientia intuitiva is an intuitive apprehension of a thing’s unique essence but suggest that knowing such an essence does not require understanding how that essence is situated in a complex nexus of other essences (Soyarslan Reference Soyarslan2016).

In the Nagelate Schriften, a posthumous Dutch edition of Spinoza’s works, there is another “formal” that appears in the description of scientia intuitiva: “from an adequate idea of the formal essence of certain attributes of God to adequate cognition of the [NS: formal] essence of things.” This “formal” might not be an insertion to be disregarded, but rather an interpolation clarifying that scientia intuitiva is an adequate cognition of the “formal essence” of things, that is, an understanding of things’ formal reality. Given an adequate idea of the formal reality of the attributes of God, one can immediately understand that things are formally real as eternal modes which can, like the substance in which they inhere, be conceived under different attributes (see Primus Reference Primus and Garberforthcoming). Scientia intuitiva may also be an understanding of how exactly a unique essence follows from God’s nature, but it is also possible that scientia intuitiva is just an intuitive understanding of things’ formal reality as in and caused by God.

Another major topic of debate is whether what is understood by scientia intuitiva can be understood by reason, the other kind of adequate cognition mentioned in the Ethics, in which adequate ideas proceed from the adequate ideas Spinoza calls “common notions” and “adequate ideas of properties” (E2p38–40s2). An example of a view on which one could come to understand the same things by either reason or scientia intuitiva was just canvassed above: through both reason – e.g., reasoning through the demonstrations of the Ethics – and scientia intuitiva, a mind can come to understand fundamental ontological structures (Primus Reference Primus and Garberforthcoming). The distinctive power of scientia intuitiva is due to its immediacy. (For other views on which scientia intuitiva and reason differ in form or method and not in content, see Yovel Reference Yovel and Yovel1989 and Nadler Reference Nadler2006.) Scholars including Curley Reference Curley and Grene1973a, Gueroult Reference Gueroult1974, and Soyarslan Reference Soyarslan2016 disagree: scientia intuitiva enables one to understand what is in principle inaccessible to reason. If, through reason, one is limited to understanding necessary properties that are common to many things, and if scientia intuitiva is an understanding of unique essences, then it does seem like the understanding conferred by scientia intuitiva goes beyond what reason could deliver.

Finally, commentators have also proposed that scientia intuitiva grants those who experience it a certain kind of self-knowledge. For example, Primus (Reference Primus and Garberforthcoming) argues that, in scientia intuitiva, one does not just immediately understand the monist ontology, but one also immediately understands oneself (and one’s own mind) as existing in that monist system. In a similar vein, Soyarslan has argued that scientia intuitiva is an intuitive grasp of “our power as a manifestation and consequence of God’s power” (Reference Soyarslan2016, 44).

Involvement (Latin infinitive: involvere) plays an important and multifaceted role in Spinoza’s thought. In the opening definitions and axioms of the Ethics, Spinoza declares that the essence of a cause of itself involves its existence (E1def1) and knowledge of an effect involves knowledge of its cause (E1a4). Involvement also plays an essential role in Spinoza’s account of the finite modes in Part 2, culminating in his claims that each idea of each singular thing involves an essence of God (E2p45), and that every idea involves a volition (E2p49). Unfortunately, “involvement” is never explicitly defined by Spinoza. As Alan Gabbey (Reference Gabbey2008) has noted, “involves” normally seems to mean “implies.” For example, when Spinoza says that a cause of itself has an essence which involves existence, he means that existence follows from its essence (E1def1). Conversely, when Spinoza denies that the essence of modes involves existence (E1p24, E2a1), he means that their essence does not imply that they exist. However, there are a number of passages which complicate this story about involvement, particularly its direction and force.

First, consider E1a4: “The knowledge of an effect depends on, and involves, the knowledge of its cause.” This axiom is famously Spinoza’s only explicit support for his doctrine of a parallelism between ideas and things (E2p7). In E1a4, Spinoza says that knowledge of an effect implies knowledge of its cause. As Margaret Wilson (Reference Wilson and Yovel1991) notes, when E2p16 uses E1a4 in its proof, Spinoza seems to take E1a4 to assert the converse as well: knowledge of a cause implies knowledge of its effects. Taken together, these dual directions of implication might have the implausible conclusion that knowledge of any effect of God gets us knowledge of God, and knowledge of God gets us knowledge of every effect of God. To avoid this conclusion, Wilson emphasizes that at least some involvement relations must be grasped only inadequately.

Second, E2p45 says that each idea of each body which actually exists necessarily “involves” an eternal and infinite essence of God. However, E2p10cs denies that the nature of God “pertains” to the essence of finite things. How could an idea involve an essence of God, and yet the essence of God fail to pertain to that idea? Don Garrett (Reference Garrett, Sorell, Rogers and Kraye2010) proposes that the solution to this puzzle is to recognize that “involvement” can sometimes go in the converse direction: for the idea of a body to involve God’s essence is for God’s essence to imply that idea of body.

Third, consider E2p49, which Spinoza glosses as showing that “singular volitions and ideas are one and the same” (E2p49c). Here, as elsewhere, the “one and the same” relation is ordinarily understood as a relation of numerical identity. However, the proof of E2p49 demonstrates only that an idea “involves” an affirmation, and that an affirmation “involves” an idea. This is somewhat puzzling, since mutual implication is not ordinarily sufficient for numerical identity. In this proof, it seems that “involves” has a stronger sense than “implies,” and rather means “belongs to the essence of” in the sense of E2def2.

Spinoza’s complex relation to Islam and the Islamic world can be charted in several ways. Although we do not have direct evidence of the influence of Islamic philosophy in Spinoza’s texts, scholars have argued for possible influence through his direct engagement with medieval Jewish philosophers. Some have argued for a wide-ranging set of parallels (Wolfson Reference Wolfson1934); others have argued for specific influences. One of these latter would be the idea, attributed to Ibn Rushd (Averroes), that there is one intellect shared by all humans, which is a view that seems to have a parallel in Spinoza’s claim that minds are modes of the infinite divine attribute of Thought and “parts” of the divine infinite intellect (E2p11c).

Another influence might be found in Spinoza’s ultimate rejection of the so-called doctrine of “double-truth,” that is, the view that philosophy and theology, even when they express contradictory truths, are nonetheless not in conflict, because (i) they are meant for different audiences (i.e., those guided by reason and those guided by faith), and (ii) they ultimately express different kinds of truth, one natural, the other supernatural. Although Ibn Rushd arguably rejected this view, his medieval Christian interpreters ascribed it to him, in their attempt to reconcile philosophy and religion through the idea that they have different, if sometimes overlapping, domains. Some have argued that Spinoza rejected the medieval Christian position and returned to Ibn Rushd’s view via his reading of medieval Jewish thinkers (Fraenkel Reference Fraenkel, Akasoy and Giglioni2013). In the TTP, Spinoza does think that reason and prophecy appeal to different audiences and have different epistemic and political modalities (TTP1–2, also 15), but he ultimately claims in the Ethics that any contradiction is only the result of ignorance or error, and that ultimately there is a single truth discoverable by reason, to which religion must conform (E5p41).

Spinoza does mention Islam itself more directly, albeit through metonymy. In his political philosophy he uses the figure of the “Turks” to stand for the Ottoman Empire, and in his discussion of religious toleration he uses “Mohammed” or the “Mahommedan church” to stand for Islam (cf. Malcolm Reference Malcolm2019). In the Preface of the TTP, Spinoza contrasts the republic, in which people are free to think and believe what they want without much interference from the state, with the despotic regime of the “Turks,” in which it is “a sacrilege even to debate religion” (TTPpref[9], iii/7). In the TP, he makes a similar disparaging remark about the “Tyrants of the Turks” who kill relatives of the monarch to preserve his sole authority (TP7.23, iii/317). However, contrary to his position in the TTP, he concedes that “experience seems to teach that it contributes to peace and harmony when all power is conferred on one man,” since “No state has stood so long without notable change as that of the Turks” (TP4.4, iii/288). In a letter to Burgh, Spinoza ironically praises the “Mahommedan church” for being even better than the Catholic Church in controlling men’s minds – because it did so allegedly without having suffered any schisms – while at the same time revealing his ignorance about the history of Islam (Ep76, iv/322a).

Nonetheless, in several places Spinoza treats Islam in the same way as he does the other revealed religions. His contemporary, Van Velthuysen, thought that this moral parity is a problem. All people recognize, he says, that the Turks follow their prophet in cultivating the virtues, but that these qualities alone, which all people potentially share, do not signify divine inspiration (Ep42, iv/218). Spinoza accepts his critic’s first point, but rejects the second. In the subsequent letter to Ostens, he writes,

While ceremonial practices and putative metaphysical beliefs may vary, the moral core of Islam is consistent with any other faith and ought to be judged accordingly.

Spinoza also figures posthumously in the notorious history of clandestine literature in the eighteenth century as the alleged author of the Traité sur les trois imposteurs (1719), which was used to justify attacks on Islam and revealed religion more generally (Popkin Reference Popkin, Curley and Moreau1990; Israel Reference Israel2001). This text claimed that all the Abrahamic religions were false, designed to manipulate the common person in the state and to benefit their religious leaders. Spinoza did suggest that Mohammed might be an impostor, insofar as he sought to deprive people of their freedom (Ep43; iv/225b). But, as we have seen, he does not think that Islam or other revealed religions are necessarily fraudulent or manipulative. Although Spinoza did not write this text, and does not agree with all of its central claims, nonetheless, his critique of superstition and very acceptance of Islam as a religion that like others has a virtuous core cemented his reputation among Christians and skeptics alike as an atheist.