Introduction

Despite the immense diversity of life forms that populate our universe, living organisms have a tautological point in common: life. Nevertheless, within a single organism, life can manifest itself in different ways or capacities and increasing levels of complexity. In this essay, we study excerpt 413b 10-20 from the second chapter of the second book of De Anima1 and analyze how Aristotle unifies different life capacities under a unique principle: the soul.

_“For now let just this much be said: the soul is the principle of the things mentioned and is delimited by them, namely, nour­ishment, perception, thought, and motion. In some cases, it is not difficult to see whether each of these is a soul or a part of a soul, and if a part, whether in such a way as to be separable in account alone or also in place; but in other cases there is a difficulty. For just as in the case of plants, some, when divided, evidently go on living even when separated from one another, there being one soul in actuality in each plant, but many in potentiality, so we see this occurring in other characteristics of the soul in the case of insects cut into two.” _2

Context

In De Anima3, Aristotle endeavors into the “most difficult affair”4, delivering a systematic philosophical account of the soul. This inquiry into the nature and properties of the soul is understood to be instrumental for a larger goal: a better understanding and knowledge of the natural world in general. By assuming insights into the soul’s nature would contribute to advancing our understanding of the natural world5, Aristotle immediately posits a strong link between the concept of the soul, the principle of life, and nature. This aim at the natural world in general also motivates an investigation into the soul’s “most common”6. His account will then not only focus on human souls but also consider a broader circle of living organisms such as plants. This investigation of the nature of the soul is therefore an exploration of the natural world itself.

Definition of the Soul

The passage at the center of our analysis appears in the second chapter of the second book of De Anima7 and builds upon the definition of the soul given in the first chapter of that same book. Aristotle defines the soul as “the first actuality of a natural body which has life in potentiality.”8 A firm understanding of this definition requires clarifying the concept of substance and its different types.

An implicit assumption about the nature of the soul is that the genus of the soul is substance. Aristotle considers different types of substances: matter, form, and the composite of both form and matter, the “this.” Matter, is understood to be receptive to form. It is a substrate that the form will shape to lead to the composite “this”. As such, matter is potentiality. Form, in contrast, is actuality. It is the cause that will give a determination to the substance. Actuality is further divided into a first and a second type, actuality in knowledge and in thinking. The first corresponds to a latent or dormant actuality that is not presently used. The second is an exerted or presently used actuality.

Recalling the definition of the soul previously elaborated, the soul is understood as the form that causes the natural body to live, the cause of life in natural bodies capable of life. A living natural body is a composite substance, the composition of a natural body and life, bound together by the soul. The soul is, in conclusion, the essence of the living natural body.

Account of Life

The definition of the soul given in the first chapter supposes an account of life. As emphasized at the beginning of chapter two of the De Anima9, the account of the soul would be incomplete if it hinged on a concept of life left unelucidated. Aristotle suggests that living beings have “nourishment, growth, and decay.”10 This particular definition of life has several implications. First, it sets a boundary between the ensouled and non-ensouled organisms. In particular, the assumption of nutrition excludes immortal life that does not rely on nutrition for survival11.

Second, because Aristotle aims to give the most common account of the soul, this definition is supposedly both a necessary and sufficient condition for life. Indeed, different levels of life, or ways of living, can be observed in the natural world, such as “reason, perception, motion, and rest with respect to place”12. Aristotle shows that nourishment, growth, and decay are sufficient because this is the only capacity he assumes plants have. If this account of life were not sufficient, plants would be denied a soul, contradicting Aristotle’s empirical intuition. This account of life is subsequently shown to be necessary by stating a nested hierarchical organization of the different ways of living. The capacity for nourishment, growth, and decay is said to be separable from the other ways of living. However, the other ways of living cannot be separated from it, highlighting the necessary aspect of this capacity. Being both necessary and sufficient, the definition of the soul that relies on this account of life is then the most common possible.

Argument

After showing that the account of life relying on nourishment, growth, and decay is both necessary and sufficient, the question of the relation between the different capacities of life mentioned earlier and the corresponding capacities of the soul emerges. Animals, for instance, are not merely alive in the sense plants are, but also have perception and touch13. How can we thus describe the coexistence of these different levels of living within a natural body, and how can the soul support this assemblage? This is the fundamental question that our passage of interest attempts to elucidate.

Aristotle starts his argumentation by recalling the different ways of life: nourishment, perception, thought, and motion. The list appears exhaustive and encompasses plants, animals, and human beings14. Aristotle states that the soul is indeed the principle of all these capacities, such that each way of living is matched with a functional capacity, or function, of the soul. Importantly, the assumption of separation of these life capacities raises the question of the nature of this separation at the level of the soul15. Aristotle dissects this inquiry into two sub-questions. The first asks if each of these soul functions represents a part of a soul or a soul in itself. The second asks if they differ in account or in place, addressing the Platonic thesis according to which parts of the soul were located in different spatial locations of the body. The questions are crucial for the generality of the definition of the soul laid out in the previous chapter. If separable coexisting souls exist, they would require a more precise and individual definition, undermining the attempt to provide a general understanding of the nature of the soul.

Aristotle brings forth multiple arguments to answer these interrogations. First, he suggests that some cases do not raise any issues in assessing the nature of the partitioning of the soul. This is the case, for instance, of the nourishment capacity. In the case of plants, this is the only capacity they have. As plants have a soul, we can deduce that this part of their soul accounts for the totality of the soul itself.

However, a difficulty arises in answering the difference in place or in account. Indeed, how to explain that the division of a plant can result in two viable yet distinct living organisms? How to account for this seemingly spatial division of the soul? Aristotle’s second argument states that each plant has “one soul in actuality but many in potentiality”16. This complements the initial definition of the soul as an actuality by considering that this actuality also brings the potentiality for its reproduction. The soul can beget new instantiations of itself under certain circumstances, such as division in plants. The thesis of non-localization of the soul is supported by the ubiquity of this potentiality in the body of the plant.

In a third line of argument, Aristotle attempts to address the difficulty of the coexistence of the different functions of the soul. In animals, nourishment and perception capabilities coexist. His argument arises again from the observation of insects being divided into parts that would continue living independently, as animals. On the one hand, it does not seem possible to divide the animals such that one part would keep living without perception, hence as a plant. On the other hand, living without the nourishment part is also excluded as it is assumed to be a necessary condition for life. Therefore, it does not seem possible to actually divide these parts of the soul at all, supporting the thesis parts of the soul that can differ in account but not in place.

These three lines of arguments support Aristotle’s thesis that the parts of the soul are not separable,they only differ in account and not in place17. The different parts are unified under a single soul that pervades the whole living body. They can be distinguished but not separated. This account is in sharp contrast with previous philosophers like Plato, who suggested a clear division of the parts of the soul, both in account and in place in distinct organs of the body18.

Nevertheless, if the above elucidates the unification question for plants and animals, it does not address the other capacity listed at the beginning of the excerpt: thought. Aristotle confesses the difficulty of the generalization to thought which appears to be an exceptional type of soul that could admit separation and localization from the other functions19. Indeed, rational thinking seems to be taking place in the brain and not in the whole body. Moreover, Aristotle compares the distinction between thought and the other functions of the soul to the difference between the everlasting and the perishable. This relates to the capacity of rational thinking of gods, who do not necessitate nourishment and thus places thinking as a different entity than the soul, more akin to the divine.

Philosophical Relevance

Despite its brevity, this passage of De Anima underlies a number of important philosophical concepts. First, the unicity of the soul pervades the whole living body and suggests a holistic view of natural living organisms, rather than a purely compartmental and instrumental view. Second, the arguments laid out by Aristotle to prove the unicity of the soul suggest a necessary interdependence between soul and body. The soul can only manifest itself through a natural body with life as potentiality. That a natural body can also contain multiple souls in potentiality further reinforces this interdependence. Only through the ensouled natural body can this potentiality can be eventually expressed. Body and soul are thus inseparable20, illustrating the materialist position of Aristotle.

Third, the whole argumentation used by Aristotle demonstrates the importance of the empirical approach. The most common account of life draws on intuition as to what counts as an ensouled being and what doesn’t21. This appears even more clearly in the examples used in the excerpt. Aristotle uses observations from the natural world, such as the division of plants and some insects to guide and legitimate his argumentation.

Last, by centering his account of soul around life, Aristotle admits plants and animals into the sphere of ensouled organisms. This privilege confers them a more important status that the one attributed by other thinkers22. This conception of the natural world leads to specific moral considerations regarding the duties of human beings towards other living organisms.

A Forest Perspective

According to Aristotle, plants embody the most common account of soul and life through their capacity for nourishment, growth, and decay. Aside from this theoretical construction, this unique position also reflects the material dependence of other life forms on plants. Furthermore, the example of the division of plants used by Aristotle in this excerpt underlines the difficulty of delimiting individual organisms. In the case of a single plant, Aristotle addresses this issue by assuming multiple souls in potentiality. Yet, in the case of forests, the observed level of interdependence of the different trees can suggest a soul at a meta-level where the whole forest is alive and contains the souls of individual trees as a potentiality23.

Furthermore, our current understanding of plant biology challenges the account of life given by Aristotle. As plants are increasingly shown to have more capacities than initially thought, the nested construction of life laid out by Aristotle might prove unnecessary, and the unicity of the soul be more strongly supported24.

Conclusion

The account of the soul given by Aristotle is built upon a particular understanding of life and its different forms. In the excerpt 413b 10-20, we analyzed how Aristotle unifies the different life capacities under a unique soul for each living body and its implications for our understanding of the natural world.

Bibliography

Aristotle. De Anima. Translated by Christopher Shields. Oxford: Oxford University Press, 2017.

Zeyl, Donald and Barbara Sattler, Plato’s Timaeu, The Stanford Encyclopedia of Philosophy (Summer 2022 Edition), Edward N. Zalta (ed.), forthcoming URL = <https://plato-stanford-edu.kuleuven.e-bronnen.be/archives/sum2022/entries/plato-timaeus/>.

Wohlleben, Peter, _ The hidden life of trees, _Greystone Books, 2016.

Notes

  1. Aristotle,_ De Anima_, trans. Christopher Shields, (Oxford: Oxford University Press,2016). ↩︎

  2. Aristotle, De Anima, 413b 10-20. ↩︎

  3. Aristotle, De Anima. ↩︎

  4. “Yet grasping anything trustworthy concerning the soul is completely and in every way among the most difficult of affairs.” in Aristotle, De Anima, 402a 9-10. ↩︎

  5. “It also seems that research into the soul contributes greatly to truth in general, and most especially to truth about nature. For the soul is a sort of first principle of animals. We aim to consider and ascertain its nature and essence, and then its properties, of which some seem to be affections peculiar to the soul itself, while others belong to animals as well because of the soul.” In Aristotle, De anima, 402a 5-8. ↩︎

  6. “Let this much be said about what has been handed down con­cerning the soul by our predecessors. Let us start anew, as if from the beginning, endeavouring to determine what the soul is and what its most common account would be.“ in Aristotle, De Anima, 412a 1-5. ↩︎

  7. Aristotle, De Anima. ↩︎

  8. Aristotle, _De Anima. _412a 28-29. ↩︎

  9. Aristotle, De Anima. ↩︎

  10. “By life we mean that which has through itself nourishment, growth, and decay.” in Aristotel, De Anima, 412a 14. ↩︎

  11. Therefore, gods, being immortal, are excluded from the definition and understood to be without a soul. ↩︎

  12. “​​We say, then, taking up the beginning of the inquiry, that what is ensouled is distinguished from what is not ensouled by living. But living is spoken of in several ways. And should even one of these belong to something, we say that it is alive: reason, percep­tion, motion and rest with respect to place, and further the motion in relation to nourishment, decay, and growth” in Aristotle, _De Anima, _413a 21-25. ↩︎

  13. “Being alive, then, belongs to living things because of this principle, but something is an animal primarily because of perception.For even those things which do not move or change place, but which have perception, we call animals and not merely alive.” in Aristotle, _De Anima _413b 1-4. ↩︎

  14. The nourishment is supposed to include plants. Animals, having perception and nourishment will also be included. Finally, human beings would have nourishment, perception and thought and are thus included as well. ↩︎

  15. Indeed, we stated earlier that the different ways of living can be separated, according to their ordering. Nourishment can be separated from perception but perception cannot be separated from nourishment. If these capacities can somewhat be separated, what separation, if any, does it entail for the parts of the soul supporting these capacities? ↩︎

  16. Aristotle, De Anima, 413b 18. ↩︎

  17. “It is evident from these things, though, that the remaining parts of the soul are not separable, as some assert. That they differ in account, however, is evident; for what it is to be the perceptual faculty is different from what it is to be the faculty of belief if indeed perceiving differs from believing and so on for each of the other faculties mentioned.” in Aristotle, De Anima, 413b 27-31. ↩︎

  18. Donald Zeyl and Barbara Sattler, Plato’s Timaeus, The Stanford Encyclopedia of Philosophy (Summer 2022 Edition), https://plato-stanford-edu.kuleuven.e-bronnen.be/archives/sum2022/entries/plato-timaeus. ↩︎

  19. “But concerning reason and the capacity for contemplation nothing is yet evident but it seems to be a different genus of soul, and this alone admits of being separated, in the way the everlasting is from the perishable.” in Aristotle, De Anima, 413 24-27. ↩︎

  20. “Therefore, that the soul is not separable from the body, or some 5 parts of it if it naturally has parts, is not unclear. For the actuality of some parts belongs to the parts themselves. Even so, nothing hinders some parts from being separable, because of their not being the actualities of a body.” in Aristotle, De Anima, 413a 4-8. ↩︎

  21. For instance, his definition of life as nourishment, growth and decay had to be made more precise in order to avoid granting life to elemental particles such as fire. Aristotle there clarifies growth as growth in “both directions and in all ways”, compared to elemental particles that would only move upwards or downwards. “For it is not the case that they grow upwards but not downwards; rather they grow in both directions and in all ways-those, that is, which are always nourished and continue to live as long as they are able to receive nourishment.” in Aristotle, De Anima, 413a 29:31. ↩︎

  22. A striking example is the one of Descartes and the animal machine. ↩︎

  23. Peter Wohlleben, _ The hidden life of trees _(Greystone Books, 2016). ↩︎

  24. Indeed, plants were said to have only nourishment, growth and decay as life capacity. If they are shown to also have perception and thought, and if the argument about the division still holds, the argument for the unicity of these life capacities is even more compelling. ↩︎