1 The Study of Living Beings Before Aristotle and Theophrastus
Aristotle and Theophrastus were engaged in a systematic study of living beings aimed at scientific knowledge. In this chapter I argue that the theoretical foundation for their articulation of this study into two main parts, animals and plants, is to be found in the results that Aristotle reached in his own research into the soul. This research was itself a remarkable innovation. While the ancient philosophical reflection on the soul started well before Aristotle, it never took the form of a systematic investigation concerned with the soul as the principle of living beings. The ultimate reason for this innovation is to be found in Aristotle’s interest in life – not an interest in this or that form of life but an unrestricted interest in all forms and manifestations of life. This interest caused him to engage in an unrestricted study of the soul as the ultimate principle or source of life. Tellingly, Aristotle criticizes his predecessors for having approached the soul by focusing exclusively on the human soul.Footnote 1 Aristotle names no names, but his most immediate and obvious critical target is Plato and his account of the soul in dialogues such as the Phaedo (also known in antiquity as On the Soul), Republic, and Phaedrus.Footnote 2 For Aristotle, Plato’s almost exclusive focus on the human soul was not only arbitrary but also a non-starter. A question that is at the heart of this chapter is how the completely unrestricted study of the soul envisioned at the outset of Aristotle’s De anima is subsequently narrowed down to the study of the soul as a principle of perishable living beings. Without a clear grasp of how this transition is negotiated, it is difficult to understand how Aristotle can justify his second major innovation: the approach to perishable living beings via separate studies of animals and plants.
To better appreciate the significance of this second innovation, we need to have at least an idea of the scientific discourse on and around life before Aristotle and Theophrastus. To this end, I propose to start by looking, briefly, at the so-called botanical excursus found in the Hippocratic work On the Nature of the Child (De natura pueri).Footnote 3 This work is the second part of a single, continuous embryological account concerned with a human being coming to be from conception to birth. The first part is advanced in the work On Generation (De genitura).Footnote 4 Very little is known about the (male) author of this embryological account in two parts. Since Hermann Grensemann, it has become common to refer to him as “author C.”Footnote 5 In addition to our two complementary works, author C produced the nosological treatise known as Diseases 4 (De morbis 4). The most recent research on the Hippocratic corpus has also ascribed to him the gynecological works Diseases of Women 1–2 (De morbis mulierum 1–2) and Infertile Women (De sterilibus), as well as On Glands (De glandulis).Footnote 6 If we accept these results, our author C turns out to be a medical expert especially (but not exclusively) concerned with women’s bodies. He emerges not only as a productive writer but also as “an important and original thinker, who occupies a pivotal place between the Presocratic thought and the research of the Academy and the Lyceum.”Footnote 7 This is pretty much all we can say about this ancient expert. Still, his scientific credentials, combined with his intellectual ambition, make him an excellent case study for how the discourse on and around plants was conducted before Aristotle and Theophrastus.
Early Greek philosophers such as Empedocles and Anaxagoras had an interest in the study of plants, but the discussion embedded in the treatise On Generation/On the Nature of the Child is the earliest extant treatment of the topic of plants in the ancient Greek scientific literature. We want to know why author C felt the need to offer a sustained treatment of plants in the context of an account of the formation and development of the human embryo. We are fortunate because our unknown author is forthcoming about his motivations for such an extended discussion. Here is how he restates his main thesis in a memorable way:
Now I shall return to the point in my account for the sake of which these things have been said on these subjects. I maintain that everything that grows in the earth lives from the moisture of the earth, and that whatever kind of moisture a particular kind of earth has in it, this same kind of moisture a plant [growing in it] will have. In the same way the little child also lives from its mother in her uterus and however much health the mother enjoys the fetus too will have. If one wishes to reflect upon what I have said concerning these subjects, from beginning to end, one will discover that the growth of things out of the earth and human growth are exactly the same [ἢν δέ τις βούληται ἐννοεῖν τὰ ῥηθέντα ἀµϕὶ τούτων, ἐξ ἀρχῆς ἐς τέλος, εὑρήσει τὴν φύσιν πᾶσαν παραπλησίην ἐούσαν τῶν τε ἐκ τῆς γῆς φυοµένων καὶ τὴν ἀνϑρωπίνην]. This is what I have said in the matter.
If we want to understand how an extended discussion on the topic of plants contributes to the embryological account offered in the treatise On Generation/On the Nature of the Child, we must take the words I highlighted in italics literally. Unless we take those words literally, our author C comes across not only as a rather undisciplined investigator but also as a hopelessly confused (and confusing) writer, with no firm grasp of the boundaries of his own project. In fact, his whole discussion of plants is controlled by the working hypothesis that human development is, from beginning to end, the same as the growth of plants. Scholars often describe this extended discussion as an “excursus.”Footnote 9 But the use of this word is far from ideal because it ends up suggesting that this stretch of text is an expendable aside. When we put ourselves in this less than ideal frame of mind, it becomes difficult for us to take the words highlighted in italics seriously.Footnote 10 At most we are willing to speak of what is going on in this passage as an attempt to develop an elaborate analogy between the growth of plants and that of the embryo in the womb.Footnote 11 But, again, there is no evidence that our author C is engaged in analogical thinking. Where we see analogous processes, he sees one and the same process at work.Footnote 12 Since he thinks the embryo to be identical to a plant, he does not adopt, let alone enforce, a clear-cut division between animals and plants. In fact, it seems important to his argument that no such division is presupposed.
For a better sense of what may license this overall approach to the study of life, we need to look at the background against which this Hippocratic work was written. There is now scholarly consensus that, at least on the topic of plants, author C was not an original thinker. His discussion is reminiscent of Empedocles’s ideas on the topic, or at least of theories that are a development along those lines. Furthermore, we cannot exclude that our unknown author also borrowed ideas and concepts from Anaxagoras, Diogenes of Apollonia, and Democritus.Footnote 13 We tend to discount authors who are not perceived as being original thinkers. In fact, they are quite helpful from a historical perspective since they can be used as a reliable entry point into the way in which a certain topic was discussed. But how was the discourse on and around life approached before Aristotle? I would like to answer this question by recalling a piece of doxography advanced at the very beginning of the work known as [Aristotle]’s On Plants:
Life is found in animals and plants. But in animals it is patent and obvious, whereas in plants it is hidden and not clear. To establish its existence requires considerable research. The question at issue is whether plants have or have not a soul and a capacity for desire, pain, pleasure, and discrimination.
Anaxagoras and Empedocles maintain that plants are moved by desire, and they assert emphatically that plants can feel and experience both pain and pleasure. Anaxagoras says that plants are animals and feel both pleasure and pain, concluding this from the fall of their leaves and from their growth.
Empedocles supposed that the two classes are mixed in plants.
Likewise, Plato maintained that plants must have desire because of the extreme demands of their nutritive capacity.
I will return to the historical significance of this remarkable work in Appendix III. Here, suffice it to say that its transmission is quite complicated. What E. S. Forster translates here is (in the words of Lotte Labowsky) “a medieval Greek translation of a Latin rendering of an Arabic text translated, probably via a Syriac intermediary, from a lost Greek original.”Footnote 14 As a result, the English translation reported above must be taken with a grain of salt. It is a bit odd to say that the classes of plants and animals are mixed in plants. This amounts to saying that X and Y are mixed in X, which is not a particularly felicitous claim. Still, the complicated transmission of our work may not be the only reason why the English translation does not sound idiomatic to us. Its author writes from within the Peripatetic tradition. It is also quite possible that this author is recycling information going all the way back to Aristotle and his lost work on plants. This may explain why he takes it for granted that animals and plants are two kinds of living beings.Footnote 15 And yet, it is far from obvious that he is entitled to project this distinction back to Empedocles. In fact, the impression is that Empedocles, like Anaxagoras and other Presocratic and Hippocratic authors, operated with a conception of life that was impervious to this distinction. This appears to be a rather thick conception of life, involving a share in cognition – minimally, in the form of pleasurable or painful perceptions and desires. This conception was emphatically not shared by everyone. Diogenes of Apollonia appears to have grouped humans and animals together and appears to have distinguished them from plants.Footnote 16 Still, this thick conception is embraced most famously in the Timaeus, where Plato ascribes life and soul to plants because they have pleasurable and painful perceptions as well as appetitive desires.Footnote 17 This is far from being an isolated claim in the Platonic corpus. In the Theaetetus, for instance, we are told that farmers work to replace pernicious perceptions in plants with useful and healthy ones.Footnote 18 Since Plato integrates this claim in his elaborate defense of Protagoras as an expert in education whose task consists in replacing bad perceptions with good ones, we cannot rule out that Protagoras himself used this example and even endorsed the view that plants have pleasurable and painful perceptions. I refrain from engaging in a discussion of the merits of this conception of life. What is relevant for my argument is that before Aristotle and Theophrastus (1) plants were regarded by many, if not most, as living beings and (2) there was a considerable debate as to the powers to ascribe to plants. In particular, (3) life could be understood in a univocal way; as a result, (4) plants could be considered full-blown stationary animals having a share in cognitive powers.Footnote 19
Independent evidence in support of what we read in the work On Plants that the tradition ascribes to Aristotle is found in a doxographical report going back to Aëtius. The latter organizes the ancient debate on and around plants as follows:
Plato [and] Thales [say that] plants [φυτά] too are ensouled [ἔμψυχα] living beings [ζῷα]. This is evident from the fact that they move to and from and hold their branches extended, and also that they yield when they are gathered together and then powerfully loosened again, so that they even pull up weights.
Aristotle [says that] they are ensouled [ἔμψυχα], but they are not animals [ζῷα]. For [he says that] animals [ζῷα] [unlike plants] have impulses and sense-perception, and some are also endowed with reason.
But the Stoics and Epicureans [say that] they are not ensouled [ἔμψυχα]. For they say that some animals [ζῷα] share in the impulsive and desiderative soul and some also in the rational soul. But plants [φυτά] move somehow spontaneously and in a way that does not involve [positing] a soul.
Empedocles says that plants [δένδρα], as first of the living beings [ζῴων], sprung out of the earth before the sunlight was spread around and before day and night had been separated. Due to the proportion present in their mixture [he says that] they contained the structure of the male and the female [within themselves]. They grow from the heat that has been separated out in the earth, so that they are parts of the earth, just like embryos in the belly too are parts of the womb. The fruits are superfluities of the water and the fire in the plants. Some have a lack of moisture, and after it has evaporated in the summer, lose their leaves, while others that have more moisture remain as they are and continue to be in bloom with leaves, as is the case for the laurel, the olive, and the palm. But the differences in flavors result from the variation of the particles of earth and of the plants, which draw varieties of flavors from the homoiomereiai of that which nourishes them, as in the case of vines. For it is the differences in the vines that make serviceable wine, but differences in the terrain that nourish them.
We too often approach doxography as an unphilosophical attempt to organize ancient views with respect to a given topic. In fact, doxography is a perfectly respectable form of philosophical history.Footnote 20 Our doxographical report is no exception to the rule: it is a philosophically minded attempt to delineate the theoretical options available at the time on the topic of the powers of plants. They are three: (1) plants are ensouled and they are ζῷα (Plato, Thales);Footnote 21 (2) plants are ensouled but they are not ζῷα (Aristotle); and (3) plants are not ensouled and by implication they are not ζῷα (Stoics and Epicureans).Footnote 22 The chapter ends with a rather longish entry on Empedocles, who reportedly considered δένδρα to be the first ζῷα to spring from the earth even before the sun started its rotation around the earth.
I left untranslated not only “ζῷα” but also “δένδρα” because both words are ambiguous. Let us focus on the second first. If one looks up this word in the new CGL, one finds that “δένδρ(ε)ον” – plural “δένδρ(ε)α” – means “tree” (either wild or cultivated). The same result is obtained if one checks the LSJ. But this cannot be the meaning that this word has in our context. Here it is used to refer to all the plants there might be, including trees. This is confirmed by what we read in the extant fragments from the Empedoclean poem. Typically, δένδρεα refers to plants in general rather than a particular kind of them – tree.Footnote 23 The term need not have a technical meaning for Empedocles. He chose this word as a pars pro toto for metrical reasons. I will return to the significance of this choice in due course.Footnote 24 For the time being, let me restate the main message conveyed in the doxographical entry on Empedocles as follows: life emerged from the earth with the spontaneous emergence of plants (δένδρα).Footnote 25 Empedocles considered plants, not just trees, to be the very first living beings (ζῷα) to appear on earth in the course of a zoogonic process that was itself inscribed in a narrative account of the origin of the world ab initio.Footnote 26
It is time to turn to the ambiguity of the Greek noun “ζῷα,” which cannot be translated consistently in our doxographical report. The noun “ζῷα” is closely related to the verb “ζῆν,” which can be rendered in English as “being alive.” If we have reasons to think that being alive is one and the same thing for all living beings, then we are entitled to say (with Plato, Empedocles, and maybe Thales) that plants (in our doxographical report either φυτά or δένδρα) are living beings (ζῷα). But this entails, in turn, finding out a core notion of life that can support the claim that being alive is the same (kind of) thing for animals and plants. If we have to rely solely on what we read in our doxographical entry, plants are credited with the ability to move themselves to the extent that they can recover their original upright position after being forced to bend.
It is impossible to establish what Thales may have said on the topic of the powers of plants. But it is not difficult to find textual evidence that Plato endorsed the view that being alive and being a self-mover are intimately connected. Consider the following passage from Plato’s Laws:
Clinias: “What you ask me is whether we are to speak of something as being alive [ζῆν] when it moves itself [αὐτὸ αὑτὸ κινῇ].”
Athenian Stranger: “Yes.”
Clinias: “How could it not be [alive if it moves itself]?”Footnote 27
The idea seems to be that all living beings (ζῷα) insofar as they are alive have the power to move themselves. On this view, plants are no exception to the rule. They too move themselves even though they do not displace their bodies in the way other living beings do by moving from one place to another. Admittedly, the evidence offered in our doxographical report for the self-motion of plants is somewhat opaque: plants move to and from (presumably when the wind is blowing) but then they return to their vertical posture, holding their branches extended. But we can easily supply additional, indeed better, putative evidence for the self-motion of plants. Think of a phenomenon such as the movement of plants in response to the variable direction of the sun (or another source of light). For someone who is working in the philosophical tradition, we are now considering such a movement (we call it “heliotropism” or “phototropism”) as a prime example of self-motion.
The claim that plants are ensouled living beings (ἔμψυχα ζῷα) finds confirmation in Aristotle, who tells us that his predecessors took ensouled beings to exhibit two conspicuous features: self-motion and cognition.Footnote 28 Aristotle goes on to say that they all (no one excluded) explained self-motion by positing the existence of a soul understood as a self-mover at the beginning of the chain of motion.Footnote 29 Aristotle takes this view to be philosophically unsatisfying because it does not explain self-motion; rather, it ends up making it a primitive (and so unexplained) fact. Furthermore, while Aristotle credits both human and nonhuman animals with the power to move themselves, he shows no inclination whatsoever to ascribe this power to plants.Footnote 30 Last but not least, he does not credit plants with cognition either (the other feature associated with being alive).Footnote 31 In the end, Aristotle thinks that we cannot engage in a fruitful study of living beings by adopting a univocal notion of life. An important consequence of this approach is the distinction of perishable living beings into animals (ζῷα) and plants (φυτά). While both animals and plants are alive, they are engaged in different ways of being alive.Footnote 32
But how different are the ways of being alive of plants and animals? Aristotle rejects the view that life is a univocal phenomenon but he does not embrace its opposite. In other words, he does not think that life is an equivocal phenomenon. I will explore what is involved in his position with a concentration on perishable life, namely life as is encountered here on earth. In this chapter and in the following one, I provide the reader with an initial answer to two questions: (1) How different are the ways of being alive of plants and animals for Aristotle? (2) Do they still allow him to engage in a study of animals and plants insofar as living beings? I plan to return to both questions in Chapter 6. It is only at that point that all the elements for a full answer will be in place. So I urge the reader to be patient. In the meantime, I invite the reader to appreciate the reasons for what looks like a new approach to the topic of life by turning to Aristotle’s systematic research into the soul.Footnote 33
2 Aristotle’s Research into the Soul
Traces of the debate I presented in the previous section can be found right at the outset of Aristotle’s De anima. In motivating the study of the soul, Aristotle states that his research has a significance that goes beyond the narrow boundaries of natural philosophy. At the same time he makes it very clear that this research contributes most obviously, and most directly, to the study of nature. What is immediately relevant to our discussion is the reason Aristotle gives for this claim:
knowledge of the soul seems to contribute greatly to all truth but especially to [truth about] nature because the soul is like a principle of living beings [ἔστι γὰρ οἷον ἀρχὴ τῶν ζῴων].Footnote 34
Right after the above passage Aristotle goes on as follows:
we are seeking to study and to know the nature and essence of the soul, and then [to study and to know] as many accidents as there are of it. Some of them seem to be affections peculiar to the soul, while others [seem] to belong also to living beings [τοῖς ζῴοις] on account of the soul.
This second passage confirms that Aristotle sees a very close connection between his research into the soul and the study of living beings. I gloss over the details of this passage, which are quite intricate.Footnote 35
What matters is my translation of ζῷα as “living beings.” This translation requires a few words of elaboration, especially since I have already argued that Aristotle uses ζῷα to refer to animals to the exclusion of plants. This is generally true. For example, Aristotle says that being alive (ζῆν) belongs to all living beings (ζῶσι), but animals (ζῷα) alone have a share in sense-perception because there is more to animals than merely being alive (ζῆν).Footnote 36 Aristotle can make this claim because his considered view is that being alive belongs in one way to animals and in another way to plants. This result follows from a theoretical commitment Aristotle makes when he famously states that “being alive [ζῆν] is said in many ways.”Footnote 37 The significance of this statement for Aristotle’s study of the soul can hardly be overstated. Aristotle expands on it by offering a list of life activities introduced by the claim that any one of them suffices for being alive: thinking, perceiving, change with respect to place, and change with respect to nutrition, decay, and growth.Footnote 38 There is a great deal that is interesting in the strategy employed at this juncture of Aristotle’s argument. To begin with, Aristotle does not try to define life or being alive. Instead, he offers us what he takes to be an exhaustive list of activities. Any one of them suffices for life. Furthermore, Aristotle does not distinguish between cognitive and non-cognitive activities; rather, he treats thinking and perceiving on a par with nutrition, decay, and growth. They are all regarded by him as life activities; as such, they are all traced back to a soul as their ultimate source.Footnote 39 Since any one of them suffices for life, Aristotle must explain how they come together in different kinds of living beings. When Aristotle says that there is more to animals than being alive, he means to say that the kind of life exemplified by animals involves, in addition to change with respect to nutrition, decay, and growth, the presence of sense-perception, minimally in the form of sense of touch. Such a life entails the ability to feel pain and pleasure as well as the ability to desire, minimally in the form of appetitive desires. All this follow, directly and immediately, from having the power for sense-perception.
Aristotle elaborates further on the way he envisions the relation between sense-perception, the ability to feel pain and pleasure, and the ability to desire in the context of his discussion of embodied cognition in DA III 7. Here Aristotle discusses how the activation of sense-perception leads an animal to pursue or to avoid something. It is emphatically not the case, Aristotle says, that an animal first perceives something pleasant or painful and then pursues or avoids it; rather, perceiving something pleasant or painful is ipso facto pursuing or avoiding it.Footnote 40 The capacity for pursuit and the capacity for avoidance are not different from one another or from the perceptual capacity; it is only their being that is different.Footnote 41 In other words, there are not three distinct powers in the animal; rather, there is only one power but this power is either taken by itself as in sense-perception or is taken in relation to how the animal reacts to that which is good (pleasant) or bad (painful) for it.Footnote 42
Unlike animals, plants are merely alive in the sense that they are barred from having a share in the higher (cognitive) powers of the soul. Aristotle separates plants from animals and makes room for a type of life that does not involve cognition – namely, plant life. It may turn out to be quite difficult for Aristotle to decide whether a certain creature is an animal or a plant. But this is an epistemic difficulty that does not preclude him from holding that a perishable creature must be either an animal or a plant. Aristotle can maintain that there is a dividing line between animals and plants even if he is not able to discern that line. His clearest pronunciation on this front is found at the outset of HA VII (VIII), where he announces that nature does not make leaps but rather proceeds by small steps to the point that we may fail to see the boundary between animate and inanimate things, as well as the boundary between plants and animals.Footnote 43 Gradualism need not entail the absence of boundaries in nature. It only means that these boundaries are hard to find. Aristotle discusses a few borderline cases in his study of animals. They are all sea creatures that are plant-like in the sense that they resemble plants. Some of these creatures are attached to rocks or other hard surfaces in the sea and cannot survive when detached (pinnas and razor-mussels are explicitly mentioned). Still, the presence of a rudimentary form of cognition in these borderline creatures is sufficient for considering them animals rather than plants.Footnote 44
The division into animals and plants cannot be presupposed at the outset of Aristotle’s research into the soul; rather, it is a theoretical achievement that is secured only in the context of this research. Moreover, it is an achievement that requires elaboration and defense. My brief review of the discourse on and around living beings before Aristotle suggests that the distinction between animals and plants was not seen, let alone shared, by everyone at the time. While Aristotle’s predecessors and contemporaries would have agreed that the soul is a source of life in the sense that it is that which distinguishes what is alive from that which is not, they would not have granted him the distinction between animals and plants. Alternatively, they would have drawn this distinction in a different way. For instance, they would have granted that plants are a different kind of living beings, but they would have insisted that plants do have a share in cognition nonetheless. A prime example for this strategy is Plato, who in the Timaeus describes plants as another (kind of) living being (ἕτερον ζῷον) different from the human being.Footnote 45 While he holds that plants do not have a share in judgment, belief, and intelligence, he grants them sense-perception and feelings of pleasure and pain accompanied by appetitive desires.Footnote 46
We can firm up the results reached so far with the help of a passage from the Epinomis, a dialogue attributed to Plato:
Athenian Stranger: When a soul and a body come together to form a single structure and produce a single form, do we assent that this is most truly said to be a living being [ζῷον].
Clinias: Yes.
Athenian Stranger: So this kind of thing is most correctly called a living being [ζῷον].
Clinias: Indeed.Footnote 47
This passage suggests that when Aristotle was about to embark on his research into the soul, a living being (ζῷον) was considered a complex of soul and body in which the soul is the ultimate source of life.Footnote 48 So Aristotle is fully justified in assuming, right at the beginning of De anima, that the soul is “like a principle of living beings.”Footnote 49 We can take this initial statement as an indistinct whole (καθόλου) of the sort described at the outset of Phys. I 1.Footnote 50 At this early stage of the argument, we are introduced to something that requires a great deal of elaboration and articulation. More directly, both “principle” and “living beings” are ambiguous. A main task of the subsequent research consists in clarifying this initial statement. Among other things, Aristotle is expected to tell us (1) what kind of principle the soul is, (2) how many kinds of living beings there are, and (3) which of them is (or are) immediately relevant to the project attempted in De anima.
The ambiguity and tentativeness of ζῷα at the outset of Aristotle’s De anima is often overlooked or minimized. I will not engage in a full review of the numerous translations of this passage.Footnote 51 I am content to single out the new translation produced by Christopher Shields for the Clarendon Aristotle Series because of its visibility and importance. Shields translates our sentence as follows: “for the soul is a sort of principle of animals.”Footnote 52 On this reading, Aristotle’s De anima may be taken to have a distinctively zoological orientation right from the start. The most outspoken defender of a zoological reading of Aristotle’s De anima is Pierre Pellegrin, who has developed an interpretation that makes it a treatise about animal psychology.Footnote 53 It is far from clear that Shields is advocating such a reading. His view seems to be that animals are mentioned at the outset of Aristotle’s research into the soul because they are the most obvious (and least controversial) example of living beings. Animals so understood include the human being. On this reading, the opening lines of De anima do not exclude that there are living beings other than (human and nonhuman) animals. Part of the task that Aristotle takes upon himself, right from the start, consists in clarifying what sort of principle the soul is, and whether there are ensouled beings beyond the most obvious case of human and nonhuman animals.Footnote 54
Such a reading ends up being close but not identical to the one I have developed so far. My view can be restated by saying that ζῷον/living being is a pre-theoretical concept. This is a concept that is not informed by the subsequent theory advanced in De anima. By contrast, ζῷον/animal is a concept isolated in the course of Aristotle’s research into the soul.Footnote 55 As such, it is a normative concept that Aristotle is expected to adopt in his study of animals. Quite tellingly, he explicitly invokes this second concept whenever it is needed or appropriate for him to do so.Footnote 56 At least in this sense, it is correct to say that the research into the soul conducted in De anima plays a foundational role for the zoological writings. This research orients, and indeed structures, the study of animals by providing the investigator with a suitable theoretical framework. More to the point: the very possibility of focusing animals to the exclusion of plants depends on adopting the normative concept introduced in De anima.Footnote 57
Let me elaborate further on Aristotle’s task as it emerges from the opening statement of his De anima. At the outset of the treatise, ζῷα can only mean “living beings.” But ζῷα is not simply ambiguous between (1) living beings, including plants, and (2) animals, to the exclusion of plants. The situation is decidedly more complicated. When, in the Epinomis, Clinias agrees to call an ensouled being a living being (ζῷον), he agrees to call a heavenly body a living being. If the reader is not persuaded that the ζῷον can be used to refer to both mortal and immortal living beings, I suggest turning to the Timaeus, where Plato says that “everything that partakes of life [ζῆν] may justly and with perfect truth be called a living being [ζῷον].”Footnote 58 Plato makes the etymological connection between life and living being as he introduces plants as another kind of living beings next to the human being. According to him, plants ought to be called living beings (ζῷα) because they partake in being alive. His polemical target is the position that denies that plants are living beings by denying that they are ensouled.
When we reflect on what Plato says on the topic of plants, we appreciate why the doxographical tradition has no qualms registering Plato as a defender of the view that plants are living beings (ζῷα). And yet, when we look at the actual use that Plato makes of ζῷον in the Timaeus, we discover that he uses it to refer to things as different as:
(1) the cosmos, which is described as an intelligent, ensouled ζῷον (Tim. 30 B 1) and a visible ζῷον containing all the ζῷα that there might be (Tim. 30 D 3–31 A 1)
(2) the fixed stars and the planets, which are described as ζῷα (Tim. 92 B 5)
(4) plants, which are collectively referred to as another (kind of) ζῷον (Tim. 77 A 5 and Tim. 77 C 3)
(5) the sexual parts of the male and the female human being, which are described as a self-willed ζῷον (Tim. 91 A 2 and Tim. 91 C 2).Footnote 59
For Plato there exist both perishable and imperishable living beings (ζῷα). Moreover, not only the cosmos but also the heavenly bodies are imperishable living beings (ζῷα). Both deserve to be called “gods” (θεοί). For instance, Plato refers to the cosmos as a blessed god (Tim. 34 B 8–9) and to the heavenly as visible gods (Tim. 40 A 1–3, Tim. 40 D 4).Footnote 60 In other words, the connection between living beings/ζῷα and gods/θεοί is explicitly made in the Timaeus.Footnote 61 With this observation in place, we can now return to Aristotle’s De anima.
Up to this point, I have placed great emphasis on the first two occurrences of the term ζῷα at the beginning of Aristotle’s De anima. However, this term resurfaces again a few lines later in the following passage:
As it is now, those who speak and research into the soul seek to study the human soul only. But we must be careful not to ignore the question whether its account is one, like in the case of living being [ζῷον], or different for each soul, like in the case of horse, dog, human being, and god [θεός]; living being [ζῷον], the universal, being either nothing or posterior.Footnote 62
Here Aristotle sets himself apart from all his predecessors. While they were mostly concerned with the human soul, he is ready to engage in research that is not programmatically restricted to any kind of soul. An obvious question for anyone who wants to embark on such an unrestricted investigation is whether the soul is a sufficiently homogeneous principle of living beings. In fact, the insertion of “god” next to “horse, dog, human being” makes the case for the heterogeneity of the soul quite pressing. To begin with, it is not at all obvious that the soul has sufficient unity to be the object of a single investigation. If the soul understood as the principle of life can give rise to vastly different ways of life, such as the life of a human being, the life of a horse or a dog, and the life of a god, one may legitimately wonder whether we can engage in an unrestricted study of the soul. Furthermore, it is not at all clear how such a study is to be conducted if the goal is to give an account of the soul that applies to human beings, dogs, horses, and gods. We should resist any easy way out of these methodological concerns. We cannot dismiss the presence of “god” next to “horse, dog, human being” by positing that this word was originally added as a marginal gloss and was subsequently incorporated into the main text. The presence of “god” in our text is dictated by the logic of ancient Greek thought: anything that partakes of life can be called a living being – a ζῷον. A god, qua living being, is no exception to the rule.Footnote 63 Aristotle goes on to says that living being (ζῷον), the universal, is either nothing or something posterior. Either option becomes attractive only if gods are regarded as living beings alongside dogs, horses, and human beings. But if so, then we may be left with no choice but to entertain the thought that “living being” (ζῷον) is a term that can be predicated of vastly different kinds of beings. In this scenario, we should therefore take very seriously the possibility that “living being” is not predicated in the way a genus is predicated of its species but in some other attenuated way to be further explored.Footnote 64
For an idea of how Aristotle would like to deal with these methodological concerns, we must jump to the beginning of the second book. There, Aristotle is no longer concerned with all the living beings that there might be. By his own admission, he is now primarily concerned with perishable living beings.Footnote 65 This restriction is already in place when Aristotle gives his most common (and non-reductive) account of the soul. For Aristotle, the soul is the first actuality of a natural, organic body that has life potentially.Footnote 66 We do not have to wonder what “life” may mean in this context since just a few lines before giving his most common account of the soul Aristotle tells us that being alive entails being able to engage in self-nutrition, growth, and decline.Footnote 67 What these life activities have in common is that they are necessary for the life of perishable living beings.Footnote 68 The obvious question is why the restriction to perishable living beings is not an arbitrary one. Since right at the outset of his investigation Aristotle has criticized his predecessors for having arbitrarily restricted their study of the soul to the case of the human being, we want to know why his own restriction is not vulnerable to the same criticism.
An answer to this question can be given by reflecting on the analogy Aristotle establishes between powers of the soul and rectilinear plane figures:
Now it is clear that there will be one account in the same way of soul and rectilinear plane figure: for just as there is no rectilinear plane figure beyond the triangle and the rectilinear plane figures ordered in the series, so here soul is nothing beyond the [powers of the soul] mentioned.Footnote 69
The centrality of the analogy between powers of the souls and rectilinear plane figures for a correct understanding of the project attempted in Aristotle’s De anima cannot be disputed.Footnote 70 Among other things, this analogy reveals that Aristotle has a plan for the study of the soul, and this plan not only dictates how Aristotle deals with the powers of the soul in the rest of the work but also helps him draw the boundaries of his own research. Aristotle argues that just as rectilinear plane figures are ordered in a series beginning with triangle, so are the powers of the souls. The first in this second series is the so-called nutritive power of the soul. The relevant powers of the soul are distributed across perishable living beings in such a way as to give rise to different kinds of souls. In other words, Aristotle can speak not only of a nutritive power but also of a nutritive soul. As a result, not only the relevant powers of the soul but also the different types of souls are ordered in a series beginning with the nutritive soul. This explains why Aristotle can say that the study of each (type of) soul is also the most appropriate study of the soul.Footnote 71
To be sure, the analogy with rectilinear plane figures provides Aristotle with a non-arbitrary method to study the relevant powers of the soul. But it also provides him with a non-arbitrary method to approach the related phenomenon of perishable life. What is alive and perishable is minimally subject to growth and decline, and neither growth nor decline are possible without engaging in self-nutrition. What Aristotle says on the topic of thought and thinking is surely relevant to a study of a life that does not include self-nutrition, growth, and decay – namely, the life of a god. According to Aristotle, there exist both disembodied (separate) intellects and heavenly bodies. Not only the former but also the latter are divine living beings engaged in thinking. So a few of the results reached in the course of the study of nous as the principle of thought and thinking can be extended to these divine living beings.Footnote 72 At the same time, however, both the life of separate (immaterial) substances such as the disembodied intellects and that of imperishable material substances such as the celestial bodies remain outside the scope of Aristotle’s De anima. From the second book onward, Aristotle’s research into the soul is programmatically restricted to the soul as a source of perishable life. As a result, this research concentrates, at least primarily, on the kinds of perishable living substances we encounter here on earth.
In the subsequent Peripatetic tradition, the study of the soul was from the very start programmatically restricted to the study of the soul of perishable living beings. In this tradition it was customary to take a shortcut by focusing right from the beginning on a particular group of living beings. Here is, for example, how Alexander of Aphrodisias introduces his own De anima:
It is our aim to speak of the soul of the body subject to generation and perishing [περὶ ψυχῆς τῆς ἐν γενέσει τε καὶ φθορᾷ σώματος]. We will discuss its substance and its powers: what they are, how many they are, and how they differ from one another. (Alexander of Aphrodisias, De anima 1.1–3; emphasis mine)
Alexander goes on to say that he finds more truth in the views passed down from Aristotle than in what other thinkers have claimed on the same topic, and that he will fulfill his stated aim by setting out Aristotle’s views on the soul as clearly as possible. Alexander is promising an account that will follow the one advanced in Aristotle’s De anima very closely. There remain a few small but philosophically significant differences. The one that matters here is how Alexander embarks on his research into the soul. He does so by restricting his investigation right from the start to the soul that is a principle of perishable life. This restriction is surely faithful to Aristotle’s thought. By now, however, it should be abundantly clear that the shortcut adopted by Alexander was not available to Aristotle. Aristotle must work his way into the position that Alexander takes for granted. Alexander can take this shortcut only because all the conceptual groundwork was already done by Aristotle.
3 Aristotle and the Study of Animals and Plants
Aristotle’s De anima provides the foundation for a theoretically informed study of life on the crucial assumption that the soul is that which distinguishes what is alive from that which is not. Aristotle’s first, and arguably most important, step in the study of life is his decision to focus on perishable life. The significance of this initial move can hardly be overstated. Given that for Aristotle there is life in the superlunary world, one may legitimately wonder whether he has developed the conceptual resources to justify his concentration on perishable life to the exclusion of imperishable life. The answer to this question is to be found in the analogy between rectilinear plane figures and powers of the souls. This analogy supplies Aristotle with a non-arbitrary method for the study of the soul as a source of life for perishable living beings.
The analogy between rectilinear plane figures and powers of the souls suggests that there are three kinds of souls. Consequently, there are three kinds of perishable life: plant life, animal life, and human life. The capacity for thought and its exercise, thinking, are a distinctive mark of the third kind of life. But while the study of this capacity is an integral part of research into the soul, it is not itself an integral part of natural philosophy. Aristotle makes this point in his general introduction to the study of animals: “one should not speak of the soul in its entirety, for it is not the soul in its entirety that is a nature but [only] some part of it (either one part or more parts).”Footnote 73 The same point resurfaces in the Metaphysics:
it is the task of the natural philosopher to study the soul to some extent, namely [to study] all [the parts of] the soul [that are] not [conceivable] without matter.Footnote 74
From what Aristotle says elsewhere, it is clear that he means to rule out the capacity for thought from the purview of natural philosophy.Footnote 75 For Aristotle, natural philosophy is concerned with the soul under a certain description – namely, the soul as the nature of a living body. This description does not apply to nous as the principle or source of human thought.Footnote 76
While Aristotle cannot accommodate nous as a principle of human thought within nature, he is able and willing to make a reference to such a principle in the study of nature. This becomes clear as soon as we realize that Aristotle explains certain features of the human body teleologically with reference to the human capacity for thought. Aristotle can consistently claim that we must refer to nous as the principle of human thought if we want to arrive at a scientifically adequate understanding of the human body, and at the same time he can maintain that nous falls outside the boundaries of natural philosophy. The explanation of the human erect posture illustrates this point very well. For Aristotle, the upright posture distinctive of the human being is for the sake of facilitating human thinking.Footnote 77 The explanation of the human tongue is another instance of the same phenomenon. According to Aristotle, the human tongue is different from that of all other animals because it is exceptionally soft and flexible to allow for human speech, which is a necessary (but not sufficient) condition for human thought.Footnote 78 Clearly, (1) the human body and its various parts are a legitimate topic for natural philosophy, and (2) a full explanation of their arrangement and functioning requires a reference to the human capacity for thought; but (3) this does not entail that this capacity falls within the realm of nature. We can restate points (1) to (3) by saying that nous functions as an explanatory principle in rendering premises relevant to the explanation of the human animal, but it is not itself a fitting object of study for natural philosophy. In due course I will argue that the human animal is not only a fitting object of natural investigation but it also plays a somewhat special role in the context of Aristotle’s study of animals.Footnote 79 For the time being, let me stress that once we remove the study of the capacity for thought from the realm of natural philosophy, we are left with two forms of perishable life: plant life and animal life, with human life as a particular kind of animal life. It is because Aristotle takes animals (human beings included) and plants to be different kinds of perishable living beings that he is justified in approaching the study of perishable life via separate studies of animals and plants.
This conclusion can be squared with the view that the human being occupies a somewhat unique place in Aristotle’s cosmos. A famous passage from DC II 12 can help us make progress on this front.Footnote 80 Here Aristotle confronts a difficulty that casts doubt on the claim that there is order in the natural world. One might expect order to entail that the things that are closer to the first unmoved principle of the cosmos engage in fewer activities, while those that are further away from that principle display an increasingly complex behavior. This is in fact not the case, either in the celestial region or in the sublunary world. For the sake of our argument we can concentrate on the sublunary world, where human beings display a vastly more complex behavior than animals and plants. Furthermore, plants are stationary living beings, and they are only engaged in self-nutrition and reproduction. Should we conclude that plants are closer to the best condition enjoyed by the first unmoved mover? Of course not.
Aristotle offers his solution to this difficulty with the help of an analogy: some people may remain fit without physical exercise; others may need little exercise to stay fit; others still may need to engage in a variety of strenuous physical exercise to attain the same goal; finally, there are also a few who must settle for a lesser goal because they can never be fit regardless of how much physical exercise they undertake. This lesser goal can be one of the very things done for the sake of the higher goal – for instance, weight loss. Losing weight when one is overweight is a necessary but not sufficient condition for fitness. But how are we expected to apply this elaborate analogy at the cosmological level? Here is the answer: while animals and plants are like those people who must settle for a lesser goal because they cannot achieve fitness, human beings are in a predicament comparable to those people who are required to engage in an elaborate scheme of action to stay fit. In this respect, human beings are different not only from higher (divine) living beings, which achieve their goal with little or no action, but also from lower living beings, which are permanently barred from achieving that goal.
Human beings enjoy a somewhat special status among perishable living beings. They alone have a share in the divine goal, which is to be understood as the exercise of the activity characteristic of imperishable (divine) living beings. This activity is theoretical thinking. When we are engaged in this sort of activity, we are active with our best part, which is also a divine part. But the exercise of this activity requires us to engage in a variety of more mundane activities. I have in mind activities such as perceiving, storing memories, and speaking a language. It does not take long to see that these more mundane activities are not on a par with theoretical thinking. They are all activities that are common to the soul and the body; as such, they cannot be adequately explained without a reference to the body. By contrast, theoretical thinking can, indeed should, be considered apart from its bodily implementation, especially if it is an activity we share with the disembodied intellects. In this sense, it exceeds the boundaries of nature. We are back to the same conclusion as before: while we cannot make sense of the complexity of human life without a reference to the human capacity for thought, nous understood as the principle that explains this capacity is excluded from natural philosophy. This exclusion makes it possible for Aristotle to subsume human life under animal life and makes it possible for him to consider human and nonhuman animals as a single investigative domain.
Separate studies of animals and plants are announced at the outset of Aristotle’s Meteorology:
It has already been spoken about the first causes of nature and all natural motion; also about the stars that are ordered in the motion of the heavens, and about the bodily elements, [establishing] how many they are and what their nature is, and how they change into one another, and about generation and perishing in general. There remains for consideration a part of this investigation that all predecessors called “meteorology.” These things are natural, although their order is less perfect than that of the first bodily element. They take place in the region nearest to the motion of the stars, such as the Milky Way, the comets, and the inflamed and moving portents. They are also the affections that we may posit to be common to air and water, and furthermore the kinds, parts, and affections of the earth, from which we might study the causes of winds and earthquakes and all the things that happen in accordance with their motions. Some of these things puzzle us, while we may be able to touch upon others in some way. Furthermore, [the investigation] is concerned with the falling of thunderbolts, with whirlwinds and fire-winds, and furthermore with the recurrent affections that are produced in these same bodies by concretion. Once we have dealt with these things, we will see whether we are somehow able to give an account, in accordance with the method indicated, of animals and plants, both in general and separately [περὶ ζῴων καὶ φυτῶν, καθόλου τε καὶ χωρίς]. Once this is done, perhaps the whole of what was established by us at the outset will be completed.Footnote 81
This passage presents us with a sketch of the study of nature as envisioned by Aristotle. Like any other sketch, this one lacks in detail. For one thing, there is no reference to the human being. For another, there is no mention of the research into the soul. It is hardly controversial that we can read a reference to the human being in our passage. Much more delicate is the absence of any explicit reference to research into the soul. This absence can be handled in more than one way. It can be explained away by saying that we are only given the main lines of natural philosophy as understood by Aristotle and saying that certain details are inevitably left out. But it cannot be ruled out that Aristotle’s research into the soul, while it has foundational character for the study of living beings, is not itself a part of natural philosophy. If so, the study of the principle of perishable life (the soul) is not to be conflated with the study of perishable life (animals and plants).
Recall the passages from PA I and Metaph. VI where Aristotle states that the power of thought and the ensuing activity of thinking go beyond the scope of natural philosophy. What Aristotle says at the beginning of his Meteorology can be taken to be additional evidence (although only negative) that the relation of the research into the soul to natural philosophy is not as straightforward as the relation of a part to the whole.Footnote 82 We may not be able to decide, once and for all, between the two exegetical options outlined above. What is certain, however, is that a chronological move is not available to us. We cannot say that the absence of any reference to the research into the soul is evidence that Aristotle wrote his Meteorology before his De anima. Even if there is no explicit mention of the research into the soul in the programmatic passage at the beginning of Aristotle’s Meteorology, it is easy to see that this research is part of the relevant theoretical background. Without the results achieved in the context of Aristotle’s De anima, we would not be able to understand why we need to study animals and plants rather than perishable living beings.
Aristotle does not only outline the main topics of natural philosophy at the outset of his Meteorology; he also lists them in a definite order. This is the order in which they are to be studied.Footnote 83 Consider the first topic: a study of the first causes of nature and all natural motion (Meteor. I 1, 338a20–21). This is a brief yet precise reference to the investigation contained in the eight books of his Physics. It is even possible to read into this description a division of the investigation offered in the eight books into two distinct pragmateiai: a study of nature and a study of motion.Footnote 84 Whether or not we accept this reading, it is uncontroversial that a general study of nature, combined with a general study of motion, serve as a sort of theoretical prolegomenon to the ambitious research that comes to an end only when we have also given an account of “animals and plants.” When we consider the commitment to the study of animals and plants within this theoretical framework, we see that there is nothing conventional about the order in which Aristotle lists the various natural investigations at the outset of his Meteorology. An optimal study of the natural world requires that the general study of nature offered in the eight books of Aristotle’s Physics be in place before we embark on any one of the specialized studies that jointly constitute natural philosophy.Footnote 85
For different reasons, I would like to argue that the order in which animals and plants are listed in the opening lines of Aristotle’s Meteorology is an indication of the order in which their study should be approached. The research in natural philosophy outlined by Aristotle ends with a study of perishable living beings, which consists of separate studies of animals and plants to be carried out in the following order: first animals, then plants. This order of inquiry is far from obvious. In fact, it is mildly surprising. Let us return, briefly, to the inquiry into the soul offered in Aristotle’s De anima. When we look at how Aristotle proceeds in the second book, we see that he ascribes nutrition, growth, and reproduction to one and the same part of the soul, the so-called nutritive (alias vegetative) soul. We also see that he engages in a study of the various parts of the soul starting from the nutritive soul. This suggests a bottom-up approach to the study of the basic powers of the soul and their corresponding life activities. Why not transpose this overall approach to the study of perishable living beings? Why not begin the study of perishable living beings with a study of plants and then move on to a study of animals?Footnote 86
My answer to the above questions is offered in the rest of this book. Here I am content to stress that studying the principle of perishable living beings (the soul) need not be the same as studying perishable living beings (animals and plants). Aristotle is not compelled to follow the strategy adopted for the study of the powers of the soul when he turns to the study of animals and plants. His reasons for the explanatory strategy adopted in the study of animals and plants must be found within that study rather than outside it. At this early stage of my argument, let me only highlight a further aspect of my overall interpretation. Aristotle assigns a paradigmatic status (as opposed to a merely heuristic one) to animals in his study of perishable living beings. His working hypothesis is that the methodological results achieved in the context of the study of animals can somehow be extended to the study of plants. The qualification “somehow” is important. Part of my task in Chapters 4 and 5 consists in clarifying how, and indeed to what extent, these results can be extended from one investigative domain (animals) to the other (plants). For the time being, let me recall one important rule of inquiry that controls Aristotle’s overall strategy: all investigations ought to start from the thing that is most developed and as such is also better in nature.
An especially clear formulation of this rule of inquiry is found in a fragment from the now lost Protrepticus:
Prior things are always more knowable than posterior things, what is better in nature [is more knowable] than what is worse: there is knowledge more of what is organized and determinate than of their opposites [τῶν γὰρ ὡρισμένων καὶ τεταγμένων ἐπιστήμη μᾶλλόν ἐστιν ἢ τῶν ἐναντίων].Footnote 87
Additional passages from the Aristotelian corpus in which the order of explanation follows the order of nature – with the order of nature having normative force over the order of exposition – can be highlighted.Footnote 88 According to Aristotle, animals are more developed, and so more complete (and more perfect), living beings than plants; as a result, we must begin our investigation of perishable living beings from them rather than from plants. Theophrastus appears to share this idea. In Chapter 4, I argue that he embarks on his study of plants on the implicit assumption that the study of animals is already in place.
In Chapter 5, I show that Theophrastus adopts explanatory strategies that are reminiscent of those that Aristotle himself employs in his study of animals. Like Aristotle, Theophrastus approaches the study of living beings via separate studies of animals and plants. Like Aristotle, he gives explanatory priority to the study of animals. By deploying analogical reasoning, Theophrastus appears to be confident that a few results reached in the context of the study of animals can be extended to the study of plants. When we take all this into consideration, we see that the Peripatetic study of animals and plants as outlined at the outset of the Meteorology betrays a definite order of inquiry: Aristotle and Theophrastus study the more complete and more perfect form of life (animals) before embarking on a study of the one that is less complete and less perfect (plants).
The epistemic principle mandating that we start our inquiry from that which is more organized and more complex need not clash with the one that requires us to begin our investigation from that which is simpler. As will become clear in due course, animals do not only display more organization and more structure than plants; they also display a more unified organization and a more unified structure than plants. We can restate this point by saying that the complexity and structure present in animals display organic unity in a better and more perfect way than the complexity and structure present in plants. I will elaborate further on this front in Chapter 3. For the time being, I would like to return to the other promise made at the outset of Aristotle’s Meteorology. Aristotle promised not only to study “animals and plants” but also to study them “both in general and separately.” These words are evidence that the complete science envisioned at the outset of the Meteorology contains separate studies of animals and plants, and that each of the two studies has a common as well as a special component. Scholars have often found the rationale for what appears to be a complex explanatory structure in PA I. There, Aristotle says that the explanation of certain features of animal life are to be sought across different kinds of animals. He adds that such explanations are required to avoid tedious repetitions. His examples are sleep, respiration, growth, decline, and death.Footnote 89
What Aristotle says in this passage is eminently reasonable. And yet, avoiding needless repetitions cannot be his sole (let alone main) motivation for this explanatory strategy. The theory of scientific explanation outlined in Posterior Analytics requires Aristotle to give explanations at the correct level of generality. This requirement is central to his explanatory project. It is only by giving explanations at the right level of generality that we can capture salient features that might otherwise be missed. What Aristotle has in mind is best illustrated by recalling a famous example introduced in Aristotle’s Posterior Analytics: we have proper knowledge of the fact that the sum of the triangle’s internal angles is equal to two right angles if, and only if, we know that this property belongs to all triangles insofar as they are triangles.Footnote 90 Since this geometrical property belongs to all triangles, it also belongs to equilateral, isosceles, and scalene triangles. But it does not belong to them in virtue of the fact that they are equilateral, isosceles, or scalene. Rather, it belongs to them because they are triangles, or else in virtue of the fact that they are three-sided figures. Aristotle employs this example to show that there is a common explanatory level beyond that of equilateral, isosceles, and scalene triangles. He argues that this common explanatory level is reached by ignoring those facts that are specific to equilateral, isosceles, and scalene figures.
The sketch outlined at the beginning of Aristotle’s Meteorology is seriously underwritten, so it is an entirely open question how much we are entitled to read into it. But we cannot rule out, it seems to me, that the explanatory principle introduced in Aristotle’s Posterior Analytics informs the study of animals and plants announced in the opening lines of his Meteorology. There is, however, a residual ambiguity. We can read these lines as containing the promise to engage in separate studies of animals and plants (to be approached in this very order). On this reading, both studies consist of a common component followed by more specific components. But we cannot rule out that these lines announce a general study of animals and plants in addition to separate studies of animals and plants. We can think of this general study of animals and plants as an analogue to the general study of triangles that is required along with narrower explanations given for the different kinds of triangles. When we are engaged in this general study, we consider animals and plants in common insofar as they are perishable living beings. As readers of Aristotle’s Meteorology, we do not know how much there is to be explained in common for animals and plants qua perishable living beings. I am centrally concerned with this question in the next chapter. Here I would like to highlight that the project of a general study of perishable life – that is, a study that treats certain aspects of animal life and plant life in common – is not ruled out by what Aristotle promises at the outset of the Meteorology. On the contrary, such a project must be taken seriously because it is mandated by the theory of scientific explanation advanced in Aristotle’s Posterior Analytics.
In this chapter we have encountered for the first time the two epistemic principles outlined in the Introduction. While the first requires us to begin our investigation into perishable life from the most complex and most determinate form of life, the second may be read as entailing that we start this investigation from the most widespread phenomenon. These principles pull us in different directions. While the first requires us to engage in an investigation into perishable life starting from animals rather than plants, the second mandates a focus on what is common to both animals and plants. At this early stage of our argument, we do not know how Aristotle resolves this tension. We only know that both principles are equally important for Aristotle. The next chapter will take our discussion to the next level by showing how Aristotle negotiates their application in the context of the so-called Parva naturalia.
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