11.1 Introduction

The concept of proper natural science is introduced in the Preface to the Metaphysical Foundations of Natural Science (1786), and it has attracted increasing interest in recent scholarship on Kant’s philosophy of physical science. I shall argue here, however, that it also plays a central role in the critical system as a whole as it develops from the first edition of the Critique of Pure Reason (1781) to the Critique of the Power of Judgement (1790) and beyond. In particular, there is an ongoing entanglement between the physical science of Kant’s day (including, especially, the science of physical chemistry) that eventually extends to all of the central aspects of his critical system – from the necessity of particular empirical causal laws to the relationship between mechanism and teleology and even to Kant’s most developed treatment of the relationship between theoretical and practical reason at the end of his critical period.

11.2 Proper Natural Science and Causal Necessity in the Metaphysical Foundations

It is clear and uncontroversial that the Metaphysical Foundations articulates principles of what Kant calls pure natural science, which directly instantiate, via what Kant calls the empirical concept of matter, the pure (transcendental) categories and principles of the understanding in the Critique of Pure Reason. Among such principles of pure natural science, in particular, are what Kant calls the three Laws of Mechanics: the conservation of the total quantity of matter, inertia, and action equals reaction. These laws are especially important, of course, because they directly instantiate the Analogies of Experience in the first Critique.Footnote ¹

What Kant calls pure natural science thus consists of synthetic a priori propositions, such as, paradigmatically, his three Laws of Mechanics. In the Preface to the Metaphysical Foundations, however, Kant also develops a distinction between pure and proper natural science, which, in my view, is of fundamental importance:

Pure natural science consists of propositions that are strictly synthetic a priori. Proper natural science, however, is the broader concept, containing pure natural science as a sub-part (as its “pure part”). Nevertheless, proper natural science, as such, still consists of necessary laws – which necessity is “inseparably attached to the concept of nature.” Proper natural science includes particular empirical laws, which, precisely in virtue of the pure part of natural science (consisting of synthetic a priori laws), still count as necessary (“only in virtue of this pure part is natural science to be proper science”).

I have argued that, just as Kant’s three Laws of Mechanics are paradigmatic of the synthetic a priori propositions of pure natural science, Newton’s law of universal gravitation is paradigmatic, for Kant, of a particular empirical law of nature that still counts as necessary in virtue of precisely its relationship to the three Laws of Mechanics.Footnote ² In particular, the law of universal gravitation is inferred from Kepler’s so far merely inductive “rules” of planetary motion, but, for Kant, it is still determined from these rules by geometry and the three Laws of Mechanics. The inference in question is thus what Newton himself calls a “deduction from the phenomena” (via geometry and the Newtonian Laws of Motion). The law of gravitation, for both Newton and Kant, is not a mere hypothesis for explaining the Keplerian phenomena, and, in this way, it now counts for both as more than merely inductive. For Kant, in particular, it now counts as a necessary and universally valid genuine empirical law of nature.Footnote ³

I have also argued that the relevant kind of necessity is precisely that characterized in Kant’s discussion in the Postulates of Empirical Thought in general of the category of necessity (KrV, A218/B265–6). Kant is here describing a three-stage procedure in which we begin with the formal a priori conditions of the possibility of experience in general, obtain perceptions of actual events and processes given in sensation, and then assemble these perceived events and processes together in a unified experience via necessary connections (notwendige Verknüpfungen) using the general conditions of the possibility of experience with which we began.Footnote ⁴

In his detailed discussion of the third Postulate (KrV, A226–7/B279–80) Kant makes it clear that he is referring, more specifically, to causal necessity and to particular (empirical) causal laws. He mentions two essentially different types of laws: “general laws of experience” (KrV, A227/B279), such as the Analogies of Experience, and “empirical laws of causality” (KrV, A227/B280) – that is, particular causal laws relating particular kinds of events. Indeed, the very concept of causality with which Kant is operating demands such a (universal) empirical law in each case: “The schema of the cause and of the causality of a thing in general is the real upon which, whenever it is posited, something else always follows” (KrV, A144/B183; emphasis added). Kant is suggesting, therefore, that the “material” necessity in question is precisely that of the causal connections among diverse events whose (objective) necessity Hume had denied.Footnote ⁵

We have seen that, for Kant, the three Laws of Mechanics in the Metaphysical Foundations are instantiations of the three Analogies of Experience – the very principles that are constitutive, for Kant, of (causal) necessity. In order to see that Newton’s law of universal gravitation is paradigmatic, for Kant, of a necessary but still empirical (causal) law of nature, we need briefly to consider the fourth or Phenomenology chapter of the Metaphysical Foundations – which, in turn, corresponds to the Postulates of Empirical Thought in general. The role of the Phenomenology, in this context, is to explain how attributions of motion and rest to bodies can be successively determined under the modal categories of possibility, actuality, and necessity – thereby resulting in a distinction between “true” and merely “apparent” motion.

Kant, on my reading, here develops a reconstruction of Newton’s deduction from phenomena of the law of universal gravitation in Book 3 of the Principia.Footnote ⁶ We begin, from the observable (Newtonian) “Phenomena” described by Kepler’s rules: the merely relative motions of the satellites in the solar system with respect to their corresponding primary bodies (the Moon relative to the Earth, the moons of Jupiter and Saturn relative to the planets in question, and the planets relative to the Sun). Since we have not yet introduced a distinction between true and apparent motions, however, the corresponding merely relative motions thus count (so far) as merely possible. At the next stage we use the law of inertia (Kant’s second Law of Mechanics) to derive inverse-square (centripetal) accelerations of its satellites directed toward each (corresponding) primary body in the solar system (the Moon toward the Earth, the moons of Jupiter and Saturn toward their primary bodies, and so on): we now have true (as opposed to merely apparent) orbital rotations in each case, which thus now count as actual. At the third stage, finally, we find both that the accelerations in question are directly proportional to the quantities of matter of the corresponding primary bodies and that such accelerations are also everywhere mutual between any two massive bodies. In accordance with the equality of action and reaction (Kant’s third Law of Mechanics), therefore, we now have what Kant calls necessary equal and opposite motions, where the accelerations of any two gravitationally interacting bodies are oppositely directed and in inverse proportion to their masses.

Finally, since each of these mutual accelerations has just been determined as necessary in accordance with the Postulates of Empirical Thought, the law of universal gravitation has itself been determined as (conditionally) necessary in the same sense – relative to (conditional upon) the initial Keplerian Phenomena from which we began. The law of universal gravitation, in other words, is determined in its connection with the actual in accordance with the general conditions of the possibility of experience: the three Analogies of Experience as further specified by Kant’s three Laws of Mechanics. The point is that, whereas Kepler’s rules are (so far) merely inductive generalizations and, as such, are not yet grounded in a priori laws of the understanding, the law of universal gravitation is grounded by applying such a priori laws to the Keplerian Phenomena. And, in precisely this way, the law of universal gravitation thereby acquires a more than inductive material necessity in the specific sense of the Third Postulate.

Kant emphasizes in the Preface to the Metaphysical Foundations that all proper natural science is grounded in pure natural science and that the latter consists in a combination of both metaphysics and mathematics (MAN, 4:469). The three Laws of Mechanics are synthetic a priori principles, because they result from instantiating the three Analogies of Experience by what Kant calls the empirical concept of matter (or body) – the concept of the movable in space.Footnote ⁷ Such metaphysical principles belong to what Kant calls special as opposed to general metaphysics, that is, the transcendental philosophy of the first Critique (MAN, 4:469–70). And, as such, they necessarily involve mathematical synthetic a priori principles as well (MAN, 4:470). Thus, for example, the law of conservation of the total quantity of matter involves a precise quantitative instantiation of the category of substance; the law of inertia involves precise quantitative instantiations of the category of causality and the predicable (derivative category) of force; and the law of the equality of action and reaction involves a precise quantitative instantiation of the category of community or interaction (Wechselwirkung). It is just this feature of special metaphysics, which, in the present case, enables a fruitful collaboration between the special metaphysics of corporeal nature and what Kant calls the “mathematical doctrine of motion [mathematische Bewegungslehre]” – where the latter is developed, paradigmatically, in Newton’s Mathematical Principles of Natural Philosophy.Footnote ⁸ Kant, in his treatise, is providing the required metaphysical principles.

An especially significant case of the relationship between the principles of general and special metaphysics is that between the principle of causality in the first Critique and the law of inertia in the Metaphysical Foundations. Kant states this law in the Mechanics as the third proposition of this chapter and appends the following “proof”:

Thus it is clear, in the first place, that this law of special metaphysics results from instantiating the more general principle of causality formulated in general metaphysics (the transcendental philosophy of the first Critique) in a way that restricts the possible causes to those acting externally (rather than internally). And, in the second place, the parenthetical insertions at the end of both the statement of the proposition and its proof make it clear that Kant takes this law to be essentially equivalent to the law of inertia formulated as the first of Newton’s three Laws of Motion in the Principia: “Every body perseveres in its state of being at rest or moving uniformly straight forward, except insofar as it is compelled to change its state by forces impressed” (Newton Reference Newton, Bernard Cohen and Whitman1999, 416). Kant’s law of inertia, like Newton’s, presupposes the concept of Newtonian impressed forces – or, in Kant’s more general terminology, externally acting causes.

Kant calls such externally acting forces – causal actions exerted by material (lifeless) substances in accordance with the law of inertia – “moving forces [bewegende Kräfte].” And, when discussing the a priori concepts of substance, causality, action, and force in the Second Analogy (in both editions of the Critique), Kant appeals to such forces as the main example of what provides the particular content, rather than the mere universal form, of an alteration of state: “For this acquaintance with actual forces is required, which can only be given empirically, e.g., the moving forces, or, what is the same, certain successive appearances (as motions), which indicate such forces” (KrV, A207/B252). Moreover, as Kant explains in a footnote to the main paragraph, the law of inertia is therefore necessarily involved: “One should well note that I do not speak of the alteration of certain relations in general, but rather of alteration of state. Therefore, if a body moves uniformly it does not alter its state (of motion) at all, but it certainly does if its motion increases or decreases [i.e., accelerates or decelerates]” (KrV, A207/B252n).Footnote ⁹

Mathematically described moving forces, appropriately determined from given phenomena by mathematics and the Newtonian Laws of Motion (or, for Kant, his three Laws of Mechanics), constitute proper natural science. And the law of universal gravitation, in particular, is thus paradigmatic of such science. An important question, however, is the scope of this kind of science and whether, more specifically, it extends beyond the Newtonian mathematical science of motion. In the Preface to the Metaphysical Foundations Kant is famously doubtful about chemistry:

Kant here finds it difficult to grant the status of proper natural science to anything not very close to the Newtonian mathematical science of motion – and not very close, in particular, to the law of universal gravitation.Footnote ¹⁰

Nevertheless, in the climactic §26 of the Transcendental Deduction in the second edition of the Critique Kant illustrates the relationship between mere perception and full-blooded experience (Footnote note 4 above) by the examples of applying the (mathematical) categories of quantity to the perception of a house and applying the (dynamical) category of causality to the transition from a state of fluidity to one of solidity in the freezing of water (KrV, B162–3). The category of causality in the second example is applied to a clearly chemical phenomenon. And, since Kant’s first example applies the categories of quantity to a perception, it seems that the second example involves (or presupposes) a quantitative characterization of this chemical phenomenon as well. It is obvious that the state transition in question involves the freezing point of water (0° Celsius). But it is also clear, I believe, that the caloric theory of heat and the states of aggregation of various kinds of substances are also salient here. By this time (1787) Kant had acquired a good understanding of Joseph Black’s conception of latent heat, where, in the example, a quantifiable measure of heat (caloric) is lost in the freezing process with no accompanying change in the temperature of the water.Footnote ¹¹ Here, in particular, we have both a quantitatively conserved substance (caloric) and a quantitative treatment of its causal action in an important change of state (solidification). This might have given Kant reason to take the prospects for a proper science of chemistry more seriously than he had before – for this science was now becoming mathematized at the empirical level without needing a Newtonian mathematical theory of motion at the (so far unobservable) micro-level.Footnote ¹²

In the following year (1788), moreover, Kant describes chemical laws in considerably less pessimistic terms than those he had used in 1786. In the second remark to Proposition II in the first chapter of the Analytic of Pure Practical Reason in the Critique of Practical Reason, Kant emphasizes that all genuinely objective laws – whether theoretical or practical – must be grounded in a priori principles. Considering the theoretical case, in particular, Kant contrasts mechanical and chemical laws as follows: “Even the rules of concordant experiences are only called laws of nature (e.g., mechanical [laws]) if one actually cognizes them a priori, or (as in the case of chemical [laws]) one assumes that they would be cognized a priori from objective grounds if our insight [Einsicht] went deeper” (KpV, 5:26).Footnote ¹³ By contrast, in the two passages touching on chemistry from the Preface to the Metaphysical Foundations (MAN, 4:468–9 and 470–1), Kant appears to have no room for (justifiable) assumptions concerning possible extensions of our insight. On the contrary, especially in the second passage emphasizing the importance of the application of mathematics in proper natural science, Kant presents us with a binary choice: either one has already “specified” a mathematical law of motions akin to the law of universal gravitation or one has not.Footnote ¹⁴ This is one of the reasons, in my view, that Kant’s 1787 discussion of the freezing of water in the second edition of the Transcendental Deduction is significant for his intellectual development. As already remarked, in particular, Kant had now acquired a good understanding of Joseph Black’s conception of latent heat in the context of caloric theory and thus a concrete example of a new kind of application of mathematics to a chemical phenomenon – one that also provides a mathematical realization of the category of substance and its quantitative conservation. There is a tension, therefore, between Kant’s initial strictly Newtonian view and a more relaxed view associated with caloric theory.

The year 1787 was an especially busy one for Kant. During his work on the second edition of the Critique of Pure Reason he was already seriously working on the second Critique, which was originally intended as an appendix to the B edition of the first.Footnote ¹⁵ Just a few weeks after completing the manuscript for the second Critique, moreover, Kant made it clear, in a letter to Karl Leonhard Reinhold in December of 1787, that the same topics on which he had lately been working so intensively had also led him to the idea of a third Critique in which the three main branches of critical philosophy – “theoretical philosophy, teleology, and practical philosophy” (Br, 10:515) – would all be united in one system.Footnote ¹⁶ It is only in this system that the two apparently incompatible realms of nature and freedom, theoretical science and morality, are to be finally successfully integrated with one another.

11.3 Mechanism and Teleology in the Third Critique

In the first three sections of the (published) Introduction to the Critique of the Power of Judgement (1790) Kant begins with the distinction between the a priori legislation of the faculty of understanding to nature on behalf of theoretical cognition and that of the faculty of reason to the will (the faculty of desire) on behalf of purely practical cognition. In the following §IV on “the power of judgment as an a priori legislative faculty” (KU, 5:179), Kant introduces a sharp distinction between determining and reflecting judgment. The former takes a general concept or principle as already given and seeks to subsume particular instantiations under it. The latter, by contrast, takes the particular as already given and seeks to find appropriate general concepts and principles under which to subsume this particular. Moreover, the distinction between determining and reflecting judgment is to be applied, first and foremost, to the problem of the relationship between universal transcendental principles of the understanding and particular empirical laws. Thus, the same problem Kant addressed in the first Critique by his doctrine of the regulative use of reason in its attempt to find systematic unity among all such empirical laws he now addresses by the idea of reflecting judgment and its new a priori transcendental principle of “the purposiveness [Zweckmäßigkeit] of nature in its multiplicity” (KU, 5:180).Footnote ¹⁷

The following §V continues the discussion of the principle of purposiveness and begins with the determining power of judgment involved in the pure principles of the understanding governing the concept of a nature in general – which principles are both a priori and necessary. Kant then observes that particular empirical laws of nature, of course, cannot be necessary in this sense: “Thus we must think in nature, with respect to its merely empirical laws, a possibility of infinitely manifold empirical laws, which are nonetheless contingent for our insight [Einsicht] (cannot be cognized a priori), and with respect to which we judge [beurtheilen] the unity of nature in accordance with empirical laws and the possibility of the unity of experience (as a system in accordance with empirical laws) as contingent” (KU, 5:183). Kant concludes, nevertheless, as follows:

Although our insight will never get to the bottom of the “lawful unity” underlying the particular empirical laws of nature, the reflecting power of judgment assumes that it is there to be found – and that we can, and indeed must, therefore seek to find it. Since to call something a “law” is thereby to attribute necessity to it, there must be a necessity to be sought (at least in principle) in the case of any particular genuine empirical law.Footnote ¹⁸

If we now turn to §58 of the Critique of the Aesthetic Power of Judgement (the first of the last three sections of this part of the third Critique), we find a striking discussion of what Kant calls “free formations of nature,” exemplified by the solidification of a fluid due to a loss of the caloric that had maintained it in its originally fluid state. Kant describes this process as one of crystallization, which he then exemplifies with the freezing of water:

Kant is now perfectly explicit about the role of caloric in this process (considered as quantifiable) as well as the concept of latent heat. Kant is also describing the process of solidification itself in mathematical (geometrical) terms, so that both the action of caloric (as a cause) and the result of this action in the fluid (as an effect) are now characterized mathematically.Footnote ¹⁹

The significance of this kind of free formation of nature, in the context of the Critique of the Power of Judgement as a whole, is clarified in the preceding discussion. Kant is here discussing the difference between aesthetic and genuinely teleological judgments. The purposiveness of the former, as we have seen, is merely formal and subjective, while that of the latter is both material and objective. The reason is that living or organic material systems, for Kant, are characterized by the specific objective processes of nutrition, growth, reproduction, and inheritance. We shall see below why, for Kant, purely mechanical processes cannot, for our particular kind of understanding, fully explain such processes – so that teleological conceptualization and explanation, in these cases, is unavoidably necessary for us. According to the paragraph immediately preceding the one quoted above, however, this is emphatically not the case for the free formations involved in crystallization:

The discussion of crystallization and the freezing of water then follows. It seems clear, therefore, that, while Kant does find a limit to the “mechanical” laws of proper natural science in biological phenomena, he finds no such limit, at this point, in chemical phenomena (at least in what we now call physical chemistry).Footnote ²⁰

In order fully to appreciate the very different ways in which Kant in the third Critique treats the two cases of chemistry and biology, we now turn to the Critique of the Power of Teleological Judgement – and, in particular, to the Antinomy of the Power of Judgement with respect to “mechanical” and “teleological” modes of explanation (§§69–78). This Antinomy, in particular, involves an apparent conflict between two (regulative) maxims of reflective judgment: one according to which “[a]ll generation of material things and their forms must be judged as possible in accordance with merely mechanical laws,” the other according to which “[s]ome products of material nature cannot be judged as possible according to merely mechanical laws (judging them requires an entirely different law of causality, namely that of final causes)” (KU, §70, 5:387). It is in the course of this discussion that Kant finally resolves the apparent conflict between mechanism and teleology to his satisfaction, and it also becomes clear, in particular, that the former is essentially framed by the conception of mechanical moving forces developed in the Metaphysical Foundations. Kant’s elaboration on the relationship between mechanism and teleology in his further reflections on the Antinomy culminates in a consideration of “the final purpose [Endzweck] of the existence of a world, i.e., of creation itself” (KU, §84, 5:434), leading up to the discussion of Kant’s “moral proof of the existence of God” with which the third Critique – and thus the critical system as a whole – concludes (§§87–91).

As first explained in §65, Kant takes properly teleological judgments to apply to a distinctive subset of natural beings, which he calls “organized [organisirten]” beings (KU, 5:372). Teleology, for Kant, is thereby employed in the conceptualization of living or organic material systems such as plants and animals. We take such systems to have a “formative power [bildene Kraft],” which is responsible for the development, maintenance, and reproduction of the special organization of material parts characteristic of the organic system in question. And, at least when judged by the standards of our understanding, this formative power cannot itself be understood as an action of “moving force [bewegende Kraft],” and thus not as a product of the mechanism of nature.Footnote ²¹ Nevertheless, Kant insists at the same time that the concept of a natural purpose is not a constitutive concept of the understanding or reason but rather a purely regulative concept of the faculty of reflecting judgment:

The “distant analogy” in question is that we consider natural ends as analogous to our own technical products, which are formed in accordance with our conscious intentions. We thereby represent these products of nature as if they had been designed by a supersensible intelligence as their “primordial ground.” Nevertheless, since we can have absolutely no theoretical cognition of such an intelligence, the ultimate motivation for even considering such a “highest ground” can only lie in practical reason.

The following paragraph goes on to consider the objective (empirical) reality of the concept of an organized being or natural purpose:

Since Kant has just said in the preceding paragraph that the concept of a natural purpose is a merely regulative concept of reflecting judgment, the “special principle” in question is introduced in accordance the faculty of reflecting judgment. What Kant is saying in the present paragraph, therefore, is that the concept of a natural purpose does have objective (empirical) reality, insofar as there do happen to exist beings in nature with dispositions for nourishment, growth, reproduction, and self-maintenance. And, although we have no theoretical cognition of the underlying cause of these dispositions by the determining power of judgment, the faculty of reflecting judgment can justify our introduction of a teleological causal principle into the study of nature, where, however, it thereby serves only as a regulative principle compensating for the necessary limitations of our properly constitutive theoretical cognition.

As we have seen, the Antinomy of the Power of Judgement (first articulated in §70) concerns an apparent conflict between two regulative maxims of reflective judgment, one governing our search for purely mechanical explanations of the generation of all material things, the other stating that there will always remain cases of material generation where purely mechanical explanations are not to be found and recommending the use of teleological explanations instead.Footnote ²² The first point Kant then makes is that there is no genuine antinomy at all (no contradiction between two incompatible principles) in the case of two such merely regulative maxims of reflecting judgment. On the contrary, the two would be genuinely antinomial only if they were mistakenly formulated as “objective” (constitutive) principles of determining judgment (KU, 5:387).

In the case of reflecting judgment, Kant continues, the purely regulative maxim with respect to mechanism has this formulation: “I should always reflect on [all events in material nature] in accordance with the principle of the mere mechanism of nature and thus investigate them as far as I can, because without taking this principle as the basis for investigation no proper cognition of nature is possible” (KU, 5:387). Since all such investigation is potentially infinite, however, we will relatively quickly arrive at a point where some other regulative principle, such as the principle of teleology, is needed to supplement the principle of mechanism for some natural forms (organized bodies). But there is no antinomial conflict here: “Reflection in accordance with the first principle [of mechanism] is not thereby abolished; it is rather requested that it be pursued as far as one can, and it is not thereby also asserted that such forms would not be possible in accordance with the mechanism of nature” (KU, 5:388) Indeed, our human reason is absolutely incapable of determining whether, “in the for us unknown inner ground of nature itself, the physical-mechanical [combination] and the combination in accordance with purposes may not cohere together in the same things in one principle” (ibid.). As Kant reiterates at the end of the following §71, therefore, there can be no incompatibility at all between the two regulative maxims (KU, 5:389).

Kant proceeds in §72 by considering the “various systems concerning the purposiveness of nature” (KU, 5:389). The main question, he says, is whether the principle of teleology is “merely subjectively valid” (as a regulative maxim), or is also “an objective principle of nature, according to which there would pertain to it, in addition to its mechanism (in accordance with mere laws of motion) yet another kind of causality, namely that of final causes, under which the first kind (that of moving forces) would stand only as intermediate causes” (KU, 5:389–90).Footnote ²³ Kant then classifies the various systems in question and argues, in the following §73 (5:392), that “[n]one of the above systems accomplishes what it pretends to do.” In particular, what Kant calls the physical system of a realism of purposes is characterized at the end of §72: “[This system] bases purposes in nature on the analogue of a faculty acting in accordance with an intention, on the life of matter (in it, or also through an animating inner principle, a world-soul), and is called hylozoism” (KU, 5:392). And the way in which Kant dismisses this alternative in the following §73 is of particular interest: “[T]he possibility of a living matter (the concept of which contains a contradiction, because lifelessness, inertia, constitutes its essential characteristic), cannot even be conceived” (KU, 5:394). So when Kant speaks of “moving forces” and “laws of motion” here he means moving forces and laws of motion as explained in the Mechanics of the Metaphysical Foundations – where the law of inertia (and thus the Newtonian concept of externally acting impressed forces) is centrally and essentially involved. Therefore, when Kant speaks of “mechanics” and the “mechanism of nature” here he specifically has in mind proper natural science as explained in the Preface to the Metaphysical Foundations. This makes good sense, for Kant, because only what he calls proper natural science can lead to full insight (Einsicht) into the necessity of particular empirical laws.Footnote ²⁴

I now turn, against this background, to the pivotal §77: “On the peculiarity [Eigenthümlichkeit] of the human understanding, whereby the concept of a natural purpose becomes possible for us” (KU, 5:405). Indeed, Kant’s elucidation of the peculiarity of our understanding also involves explaining, in a certain sense, how it makes teleology (and thus the concept of a natural purpose) necessary for us. Kant has already stated in §71 that, although “we can in no way prove the impossibility of the generation of organized natural products through the mere mechanism of nature” (KU, 5:388), “it is just as indubitably certain, relative to our cognitive faculty, that the mere mechanism of nature can supply no explanatory ground for the generation of organized beings” (KU, 5:389; emphasis added). Moreover, in §75 he has similarly but more dramatically made the following famous claim:

The question then inevitably arises as to the basis for this (negative) certainty, and the task of §77 is finally to make this clear. It lies, as Kant suggests, not so much in the nature of the objects in question as in the nature of our specifically human understanding.

The main idea to which Kant appeals in elucidating this “peculiarity” of our understanding is a contrast between the character of our human understanding, in proceeding from the “analytically universal [Analytisch-Allgemeinen] (from concepts) to the particular (to the given empirical intuition),” and the character of another quite different understanding, “which, because it is not discursive like ours but intuitive, proceeds from the synthetically universal [Synthetisch-Allgemeinen] (from the intuition of a whole as such) to the particular, i.e., from the whole to the parts” (KU, 5:407). Two pages earlier, moreover, Kant suggests that the idea here is analogous to one already used in the first Critique in elucidating the special character of our human intuition by contrast with “another possible intuition” – so as then to take “our intuition as a particular kind, namely one for which objects are valid only as appearances” (KU, 5:405). And, two pages after drawing the contrast between the analytically universal procedure of a discursive understanding like ours and the synthetically universal procedures of an intuitive understanding (407), Kant illustrates the synthetically universal procedure in question by “the unity of space” – which although it is “no real ground of [natural] generations but only their formal condition,” still has “some similarity with [such a real ground], in so far as no part within it can be determined except in relation to the whole (whose representation thus lies at the basis of the possibility of the parts)” (KU, 5:409). It seems clear, moreover, that the property of space at issue here is the one appealed to in the third argument of the Metaphysical Exposition of the Concept of Space in the Transcendental Aesthetic of the first Critique. Space is not a “discursive, or, as one says universal [allgemeinen] concept” but a “pure intuition,” because “one can only represent a single space, and, if one speaks of many spaces, one understands them as only parts of one and the same unique [alleinigen] space[; t]hese parts can also not precede the single all-encompassing [allbefassenden] space as its constituents (out of which a composition [Zusammensetzung] would be possible), but [can] only be thought within it” (KrV, A25/B39).

In §77 of the third Critique, however, what is primarily at issue is Kant’s contrast between our discursive understanding as proceeding in an analytically universal fashion and our synthetically universal pure intuition based on a geometrical part-whole relationship between a region of space and a larger such region. But the latter also involves, in the context of natural teleology, a causal-dynamical relationship between a spatial part of an organized body in nature (e.g., an organ) and the material whole (organism) of which it is a (spatial) part. While our discursive understanding can only proceed from a part to a greater whole, the very concept of an organized (i.e., organic) body requires that there be a special kind of “reciprocal [wechselseitig]” causal relationship among each part, the whole, and all the other parts. And it is only in virtue of this property of organized bodies that they function as “self-organizing” (and “self-reproducing”) beings.Footnote ²⁵ Kant therefore contrasts a discursive understanding like ours with an intuitive understanding as follows in §77: “In accordance with the constitution of our understanding, by contrast, a real whole of nature is to be regarded only as the effect of the concurrent moving forces of the parts” (KU, 5:407; emphasis added). His point, therefore, involves precisely the concept of “mechanical moving forces” developed in the Metaphysical Foundations. So, once again, the concept of proper natural science plays a central role in Kant’s argument.

But “mechanical moving forces,” as we have seen, conform to Kant’s Second Law of Mechanics, and therefore involve only external causal influences – between one body or part of a body and others external to it. There can be no reciprocal such causal influence between a part and a whole of which it is a part. And it is for precisely this reason, for Kant, that mechanical interactions in accordance with proper natural science can never explain the generation and properties of self-organizing and self-reproducing organized beings. So, since our understanding is discursive, the only way that we can even think such a possibility is by invoking another kind of understanding, completely different from ours, that is itself intuitive rather than discursive. Due to the same “peculiarity” of our understanding, however, we – unlike the intuitive understanding itself – can never think or conceive the relevant mode of generation in which the whole is the ground of all of its parts except by thinking of such an intuitive understanding as producing or creating this whole through an idea or representation of its purpose. We must conceive the intuitive understanding as intentionally (and thus teleologically) productive of the organized body on analogy with our own intentional production of artifacts.

11.4 The Bridge between Nature and Freedom

The Antinomy of the Power of Judgement occupies §§69–78 of the third Critique. It is followed by a final discussion on the Methodology of the Teleological Power of Judgement occupying §§79–91. This final discussion culminates in the moral proof of the existence of God with which both the third Critique and the entire critical system conclude (at least as it stood in 1790). The second section of the Methodology (§80) is entitled “On the necessary subordination of the principle of mechanism to the teleological principle in the explanation of a thing as a natural purpose” (KU, 5:418). Kant begins by asserting that, although our authorization to seek for mechanical explanations is unlimited, we are nevertheless bounded by the capacity of our particular understanding for comprehending the organized beings that actually exist. We therefore require, in particular, fundamental teleological principles of original organization.

In §80 of the Methodology, however, Kant is by no means dogmatic about the latter claim. The fifth paragraph of §80 envisions an “archaeologist of nature,” who hypothesizes a “universal mother” from whom all organized creatures have emerged – the “maternal womb of the earth, which has just emerged from a condition of chaos” (KU, 5:419). Kant continues:

Kant explains in the footnote that his negative judgment concerning the possibility of a generation of organic from inorganic matter ultimately rests on nothing more nor less than the fact that this kind of generation, “so far as our empirical knowledge of nature extends, is nowhere to be found” (KU, 5:420n). But the judgment in question is not simply that, as a matter of brute contingent fact, no such generation has yet been discovered. For Kant takes “our” empirical knowledge to be limited in principle by the nature of our human understanding, which is by no means contingent from our point of view. From the point of view of the intuitive or archetypal understanding proceeding in accordance with “synthetic universality,” however, it is contingent: there can be no proof from this point of view that the problematic form of generation is absolutely impossible.

In the fourth paragraph of §80 Kant emphasizes that an “analogy of forms” among many different animal species, in terms of skeletal structure, for example, or other such systematic relationships among other bodily parts (e.g., organs), “allows the mind an at least weak ray of hope that something may be accomplished here with the principle of the mechanism of nature, without which there can be no natural science at all” (KU, 5:418). Kant concludes:

This striking passage appears to be the closest Kant ever comes to suggesting that organized beings may possibly be generated by mechanical laws. As we have seen, however, Kant cancels this possibility for us. Indeed, in his earlier discussion of crystallization in §58, toward the end of the Critique of the Aesthetic Power of Judgement, Kant has made it perfectly clear that this process is quite unproblematically mechanical.Footnote ²⁶ And it is especially striking, in particular, that Kant, at the beginning of his climactic discussion of the Methodology of Teleological Judgement, recurs again to his earlier (and more detailed) discussion of crystallization located in an analogous position toward the end of the Critique of the Aesthetic Power of Judgement. Kant’s mature view of the relationship between what we now call physical chemistry and the sciences of life is therefore an important component in his mature view of the latter sciences.

The centerpiece of Kant’s teleological Methodology features a juxtaposition of natural and moral teleology. And it is found most explicitly in the transition from §83, on the ultimate purpose (letzten Zweck) of nature as a teleological system, to §84, on the final purpose (Endzweck) of the existence of a world, that is, of creation itself.Footnote ²⁷ The ultimate purpose of nature as a teleological system (§83) involves a systematic relationship among all the organized beings (plants and animals) in nature, where, on Kant’s view, human beings are the only such organized beings that can possibly constitute the ultimate natural purpose of the whole system. This, for Kant, is because only human beings are capable of representing purposes to themselves and then acting in accordance with them. But what human end or purpose is capable of organizing the totality of this being’s purposes? Kant argues that the only two possibilities at this point, where we are restricting ourselves to purposes that can be found within rather than beyond nature, are happiness and the cultivation of a human being’s rational capacity to set and pursue arbitrary ends. Since the content of happiness varies widely (and indeed arbitrarily) among different human beings, however, the cultivation of rationality – prudential rationality as such – is the only determinate purpose that can be pursued by all.

In §84, by contrast, we are considering the final purpose (Endzweck) of the existence (and creation) of the world. This purpose is final in the sense of being unconditional, and there is absolutely nothing within nature that is not conditional on something else. For Kant, therefore, the only possible final purpose, in this sense, is the Highest Good unconditionally commanded by morality, that is, by pure practical reason itself:

It is in the crucial transition from prudential to pure practical reason, therefore, that we move from nature to freedom – and, accordingly, not only conceive the ultimate purpose of nature as a teleological system, but also become (morally) worthy of occupying the position of ultimate purpose as part of our very highest purpose: the Highest Good in the world.

But how do we move from the cultivation of prudential rationality to pure practical reason, from §83 to §84, from nature to freedom? Toward the end of §83 Kant is emphasizing the problem of “unsocial sociability” discussed earlier in his Idea for a Universal History with a Cosmopolitan Aim (1784). Here Kant, following Rousseau, is considering the rise of inequality in all forms of human progress, all of which are necessarily communal.Footnote ²⁸ The problem is to explain how the fearsome inequalities inevitably resulting from our unsocial sociability can be mitigated. One idea stems from the social contract tradition via an “invisible hand” explanation, which begins with self-interested, purely prudential rationality and arrives at a just society as the only possible solution (for prudential reason) of the problem of ever-worsening inequality. Kant, however, is not, in the end, completely satisfied with this kind of explanation, and he pursues in addition the idea of a gradual social cultivation of our specifically moral capacities – an education of the sentiments also inspired by Rousseau.

This idea is developed in the final paragraph of §83 focusing on “a purposive striving of nature towards an education or cultivation [Ausbildung], which makes us receptive to higher purposes than nature itself can afford” (KU, 5:433). The paragraph ends by invoking the special kind of pleasure that is characteristic, for Kant, of aesthetic experience:

There appears to be no doubt that the “higher purposes” in question are those unconditionally commanded by morality, that is, by pure practical reason, so that now, at the moment of transition from §83 to §84, we stand at the very doorstep of morality.

This, of course, is only the beginning of Kant’s Rousseau-inspired conception of the moral education of our natural sentiments, but here is not the place to develop it further. So I shall conclude, rather, by calling attention to an important point of agreement between this argument from the third Critique and Kant’s earlier discussion in the Groundwork of the Metaphysics of Morals (1785) of a Kingdom of Ends – a point that further emphasizes the importance of his bridge between natural and moral teleology. Kant introduces the Kingdom of Ends as a variant of the formula of autonomy, namely: “The concept of each and every rational being, which must consider itself through all the maxims of its will as universally legislating, in order to evaluate itself and its action from this point of view [the principle of autonomy], leads to a very fruitful concept depending on it, namely that of a Kingdom of Ends” (GMS, 4:433).

Kant further characterize this last concept, that of a Kingdom of Ends, as follows:

And he rounds off his introduction of this concept by giving even more prominence to the formula of humanity:

Thus Kant here emphasizes that the Kingdom of Ends is not only a procedural device for “abstract[ing] from the personal differences between rational beings” in order to arrive at truly universal moral laws but also an end (in itself) to be pursued.

Kant explicitly links the idea of a Kingdom of Ends with that of a Kingdom of Nature a few pages later in the Groundwork. He is considering a progression of three subsidiary variants, corresponding to the three categories of quantity, of the original universal formula of the categorical imperative reached at the end of the first part of the Groundwork. The third variant (the Kingdom of Ends) corresponds to the category of allness or totality, and it thereby corresponds, Kant says, to

What is most important in this context is the footnote Kant attaches to the juxtaposition of the Kingdom of Ends with a Kingdom of Nature:

This explanatory footnote in the Groundwork appears to fit very well with the transition from §83 to §84 in the third Critique. Section §83 belongs to natural teleology, and, as such, it considers a teleological organization of the whole of nature under a hierarchical system of purposes. In this sense, the ultimate purpose of nature as a teleological system is a theoretical idea for (teleologically) explaining that which exists under the superordinate purpose (or purposes) of the human species – which, for Kant, do not yet amount to the specifically moral purposes prescribed by pure practical reason. In §84, by contrast, Kant is considering the final purpose of the existence of a world, that is, of creation itself. And this, as we have seen, can only be the Highest Good in the world – an ideal of pure practical reason that we can asymptotically approach through our own “deeds and omissions” but never completely attain. Nevertheless, this idea of pure practical reason functions precisely to guide our actions in nature toward the Highest Good as much as it can or, more precisely, as much as we can embrace it.

That Kant is here constructing a bridge between nature and freedom means that the resources of both theoretical natural science and practical moral philosophy are implicated in his momentous intellectual pursuit. What I have attempted to show in this chapter is that and how the changing status of physical chemistry in his critical system – a development revealed in the history of this science in the years 1781 through 1790 and beyond – is inextricably entangled with the parallel development of Kant’s philosophy as a whole, including, in particular, his moral philosophy.Footnote ²⁹ Just as he had to deny knowledge in order to make room for (practical) faith, Kant had also to make room for physical chemistry within proper natural science while simultaneously elevating natural teleology to the status of an unavoidable part (the first part) of his long-sought-for philosophical bridge.