Lecture 1 — The definition of the soul

Thus far, we have spoken of what our predecessors handed down to us about the soul. But let us now reopen the inquiry from the beginning and endeavor to determine what the soul is and what is its most comprehensive account.

Now, we say that one of the kinds of things that are is substance. Of this, there is one thing, matter, which as such is not this particular thing; another, the form and species, according to which it is right away called “this particular thing”; and a third, that which is from both of these. Matter is, indeed, potency, and species, actuality; and this latter has two modes, one like knowledge, the other like thinking.

Bodies especially seem to be substances, and, among these, natural bodies, for these are the principles of the others. Of natural bodies, some have life, while others do not. We mean by “having life” that a thing can, through itself, take nourishment and grow and decrease.

Therefore, every natural body sharing in life will be a substance, but this sort will be substance as a composite. Since, however, it is a body, and a certain sort of body, for it is one having life, the soul will certainly not be the body. For the body is not one of the things that is in a subject; rather, it is as the subject and the matter.

It is necessary, then, that the soul be a substance, in the sense of the species, of a natural body having life in potency. Now, substance is act; it will, therefore, be the act of a body of this sort.

Now, this can mean one of two things: one, as is knowledge; another, as is thinking. It is plain, then, that it is like knowledge. For the soul remains in the body whether one is asleep or awake; whereas being awake is proportional to thinking, sleep to knowledge that is not in use. Now, knowledge is prior in the order of generation, in one and the same thing. The soul, therefore, is the first act of a natural body having life in potency.

However, such a body is anything organized. Even the parts of plants are organs, though very simple—the leaf is the covering of the pod, and the pod of the fruit; roots, too, are like mouths, for both draw in nourishment.

If, then, one should speak about something common to every soul, the soul will in fact be the first act of an organized natural body.

Hence, it is unnecessary to ask whether the soul and body are one, any more than whether the wax and the impression sealed on it are one, or in general, the matter of anything whatever and that of which it is the matter. For while “one” and “being” are predicated in many ways, that which is properly so is act.

211. Thus far, we have spoken (412a3). Having reviewed, in book 1, other men’s opinions on the soul, Aristotle now begins book 2 of his treatise, in which he sets out what he himself holds on the matter.

First, then, continuing what has gone before, he states his general aim;

and second, at now we say that one (412a6; [212]), he starts to carry it out.

He begins by saying that, despite all which has been handed down by our predecessors of the soul, it is necessary to go back to the beginning, as it were, to determine to the truth. The subject is so difficult that it is wiser to assume that the truth about it has not yet been discovered.

And in answer to the question raised in the introduction to book 1, (Bk. 1, lect. 1, nn. 10–13.) whether one should first define the soul, and afterwards its parts, he decides now to say what the soul is, which will make the very essence of the soul known, before coming to conclusions about its parts or powers. As though explaining this decision, he adds that we shall thus have acquired the most comprehensive account of soul. For when one shows what the soul is, one treats what is common, whereas when one determines each of its parts or powers, he treats only some special aspect of soul. And as he explains at the beginning of the Physics, this is the order of teaching: to begin with common things and end with things less common. (Aristotle, Physics 1.1, 184a23–24; cf. Aquinas, Commentary on Physics, bk. 1, lect. 1.)

212. Beginning, then, at now we say (412a6), his treatment divides into two parts.

In the first, he shows what soul in general is;

and in the second, starting at of the soul’s powers (414a29; [279]), he shows what are its parts or powers.

The first part subdivides into two.

In the first, he gives the definition of the soul that is like the conclusion of a demonstration.

In the second, he gives the definition of the soul that is like the principle of a demonstration, at since it is from things uncertain (413a11; [245]).

Note in passing that any definition, as he says in Posterior Analytics 1, is either the conclusion of a demonstration (for example, “thunder is a continuous noise in the clouds”) or it is the demonstration’s principle (for example, “thunder is the extinction of fire in the clouds”) or it is the demonstration itself but in a different order (for example, “thunder is a continuous noise in the clouds caused by the extinction of fire in the clouds,” in which the demonstration’s conclusion and principle both appear, though not in syllogistic order). (Aristotle, Posterior Analytics 1.8, 75b30–32; cf. Aquinas, Commentary on Posterior Analytics, bk. 1, lect. 16.)

The first part is divided into two.

In the first, he posits a first definition of the soul;

in the second, at it has been stated then (412b9; [235]), he gives an explanation of the definition.

The first is divided into two.

In the first, to clear the grounds so as to seek the soul’s definition, he makes some preliminary distinctions.

In the second, the defining proper begins, at therefore every natural body (412a15; [220]).

213. It should be noted here that, according to the Philosopher in Metaphysics 7, there is this difference between defining substance and defining accidents: in the former case nothing extrinsic to the substance being defined is included, for every substance is defined through its own material and formal principles; but in defining an accident, something outside the essence of the thing defined is referred to, that is, its subject—for the subject must be placed in the definition of the accident, as when one says, “snubness” is curvature of a nose. (Aristotle, Metaphysics 7.1, 1028a20–b2; 7.4–5, 1030b14–1031a14; cf. Aquinas, Commentary on Metaphysics, bk. 7, lect. 1, nn. 1253–58; lect. 4, nn. 1335ff.) The reason is that a definition must express what a thing is, and while substance is something complete in its being and its species, accidents do not have complete being, but rather being dependent on substance.

In the same way, no form as such is a thing complete in species; rather, completion in species belongs to the composite substance; so the composite substance is so defined that nothing is placed within its definition that is outside its essence, while something is placed within the definition of a form that is outside the form’s essence, that is, its proper subject or matter. Hence, since the soul is a form, within its definition one must place its subject or matter.

214. So, in the first part of this section, he makes certain distinctions necessary for investigating what is placed within the soul’s definition for the sake of expressing its essence, and then, at bodies especially seem to be substances (412a11; [217]), things necessary for investigating what is placed in the soul’s definition for the sake of expressing its subject.

As regards the former point, he alludes to three distinctions.

The first of which is that of being divided into the ten categories; this he hints at when he says that substance is reckoned to be one of the kinds of things that are.

215. The second distinction alluded to is that of substance into matter, form, and the composite of both. Matter is that which is as such not this particular thing (412a6) but is in mere potency to be this particular thing. Form, however, is that by which right away this particular thing is actual. And the composite substance is this particular thing; for that is said to be a particular thing which is something demonstrated, complete in existence and species; and among material realities, only the composite is such. For although separated substances are not composites of matter and form, they are still particular things, since they are actually subsisting and complete in their own nature. However, the rational soul in a certain respect can be called a particular thing—insofar as it can subsist through itself; but because it does not have a complete species, but is more part of a species, being a particular thing does not altogether belong to it. Matter, then, differs from form in this, that it is a being in potency, whereas form is the entelechy or act by which matter comes to be in act; whence the composite itself is the being in act.

216. Third, he distinguishes two senses of “act”: in one sense, as knowledge is an act; in the other, as thinking is an act. And the difference can be understood by relating these acts to their potencies. Before one acquires the grammatical habit and becomes a grammarian, whether by learning or by discovery, one is only potentially so; and this potency is reduced to act when someone has the habit of knowledge. But then again he is further in potency to the use of the habit when he is not actually thinking; and as regards this potency, he is reduced to act when he actually thinks. In this sense, then, knowledge is one act and thinking another.

217. Then, at bodies especially (412a11), he alludes to three distinctions which are presupposed by his inquiry into the meaning of the definition of the soul, so far as the subject endowed with soul is concerned.

The first distinction is that, of substances, some are bodies and some are not bodies. Among these substances, bodily substances are the most manifest: for whatever the incorporeal substances are, they are not manifest, since they are remote from our senses and are only discoverable by an exercise of the reason. Hence, he says that bodies especially seem to be substances.

218. The second distinction is between physical or natural bodies and certain non-natural bodies, artificial ones. For man and wood and stone are natural bodies, but a house or a saw is artificial. And of these, the natural bodies seem to be the more properly called substances, since natural bodies are the principles of artificial bodies.

For art works upon materials furnished by nature, but the form that is brought about by the art is an accidental form, such as a new shape and so forth. Whence artificial bodies are not in the genus of substance through their form, but only through their matter, which is natural, so they have it that they are substances from the natural bodies. Natural bodies, therefore, are substances more than artificial bodies are, for they are substance not merely on the side of their matter, but also on the side of their form.

219. Third, he distinguishes between natural bodies that have life and ones that do not. For that is said to have life which can through itself have nourishment and grow and decrease.

Note here that this explanation is said by way of example rather than definition. For besides growth and decrease, living things may exhibit sensation and intellectual knowledge and other vital activities. Whence in separated substances, as is proved in the Metaphysics 11, there is life because they have understanding and will, though they cannot grow and do not take nourishment. (Aristotle, Metaphysics 12.5, 1071a2; 12.7, 1072b26–30; cf. Aquinas, Commentary on Metaphysics, bk. 12, lect. 4, n. 2476; lect. 8, nn. 2536–44.)

But because among the things that are generated and corrupt, the soul that is in plants (to which pertains nutrition and growth, as was said at the end of book 1) is the principle of life, this is why he explains by example what has life as what has nourishment and growth. (Bk. 1, lect. 14, n. 210.) However, the proper account of life is that something is naturally apt to move its very self, taking “movement” in its wide sense so as to include intellectual activity, which is said to be a certain movement. For we say that those things are without life which are moved only from an exterior principle.

220. After this, at therefore every natural body (412a15), he begins to define the soul, presupposing the distinctions already made. And his inquiry here has three parts.

First, he inquires into the elements of the definition taken separately;

second, at if, then, one should speak about something common (412b4; [233]), he states the definition;

third, at hence, it is unnecessary (412b6; [234]), he uses it to refute an objection.

Concerning the first, he does two things.

First, he deals with the elements that pertain to the soul’s essence;

and second, to those that refer to its subject, at however, such a body is anything organized (412a28; [230]).

Concerning the first, he does two things.

First, he considers the statement that the soul is an act;

and second, at now, this can mean one of two things (412a22; [227]), he considers the statement that it is the first act.

His first conclusion, then, in line with what has been said already, is that since natural bodies seem to be substances in the fullest sense, and every body that has life is a natural body, one must say that every body that has life is a substance and, since it is a being in act, it must be a composite substance. But because to say “body that has life” is to say two things, that it is a body and that a certain sort of body, that is, one that has life, it cannot be said that the part of the body that has life, which is called the “body,” is the soul. For by “soul” we understand that by which what has life is alive; it must be understood, therefore, as something existing in a subject (taking “subject” in a broad sense to include not only those actual beings that are subjects of their accidental modifications, but also the first matter, which is a potential being). But the body that receives life rather is as the subject and matter, not in a subject.

221. Since, then, there are three sorts of substance: the composite, matter, and form, and since the soul is neither the composite itself (the body that has life) nor its matter (the body underlying the life), what is left in the path of division is that the soul is a substance as form or species of a certain sort of body, that is, a natural body having life in potency.

222. Note that he does not say simply “having life” but “having life in potency.” For “a body that has life” is understood to be the living composite substance; and the composite is not placed in the definition of the form, but its matter is. On the other hand, the matter of a living body stands to the body’s life as a potency to its act; and the soul is precisely the actuality whereby the body is alive. It is as though we were to say that shape is the actuality not of the actually shaped body—for this is composed of the shape and the body—but rather of the body as subject to shape, which body is related to the shape as potency is related to act.

223. But lest it be thought that soul is an actuality in the manner of any merely accidental form, he adds that it is substance as act, that is, as a form. And since every form is in a determinate matter, it follows that the soul is the form of a sort of body, of the sort described.

224. Note that the difference between accidental form and substantial form is that, whereas the former does not make a being in act, simply speaking, but only a being in act this way or so much—for example, as big, or as white, or something of this sort—whereas the substantial form make it exist simply speaking. Hence, the accidental form comes to a subject actually already existing, but the substantial form does not come to a subject that is already actually existing, but to one existing only in potency, that is, to prime matter.

That is why it is clear that there cannot be more than one substantial form in any one thing; for the first would make the thing an actual being, simply speaking, and all others would come to an already actually existing subject; whence, they would come to it accidentally; for they would not make a being in act simply speaking, but a being in act in a qualified sense.

225. We can therefore reject the view of Avicebron (in the book called Fons Vitae) that there is an order of several substantial forms in one and the same thing that follows the order of genera and species. Thus, an individual man would have one form whereby he is a substance, another whereby he is a body, another whereby he is an ensouled body, and so on. For according to what we have said we must say that there is one and the same substantial form whereby this individual is this particular thing or substance and whereby he is a body and an ensouled body and so on. For the more perfect form can give to matter all that a less perfect form gives and more. Whence the soul makes not only substance and body exist (as even a stone’s form does) but also makes that body be ensouled. We must not think, therefore, that the soul is the act of the body and the body is its matter and subject in such a way that the body is constituted by one form that makes it be a body and that the soul supervenes on it, making it be a living body—but rather, that the body both exists and is a body and is a living body is due to the soul. But the fact that it is a body, which is more imperfect, is as material relative to life.

226. Therefore, when the soul departs, specifically the same body is not still there; for the eyes and flesh of a dead man, as is shown in Metaphysics 7, are not called eyes and flesh except in an equivocal way. (Aristotle, Metaphysics 7.10, 1035b24–2; cf. Aquinas, Commentary on Metaphysics, bk. 7, lect. 10, nn. 1484–97.) For when the soul leaves the body, another substantial form succeeds it, one that gives it another specific existence; for the corruption of one thing does not exist without the generation of another.

227. Then, at now, this can mean (412a22), he examines the second term in the definition. He observes that there are two sorts of act, as we explained above, one is as knowledge and another is as is thinking. And it is plain that the soul is like knowledge; for it is due to the soul’s being present that an animal is able to be both asleep or awake; and being awake is similar to thinking (for just as thinking is a use of one’s knowledge, so being awake is the use of one’s senses), but sleep is more like possessed knowledge when someone is not active relative to it, for in sleep an animal’s powers are at rest.

228. Now, of these two actualities, knowledge is prior in the order of generation in one and the same thing; for it stands to thinking as potency to act. But by nature act is prior to potency (as is said in Metaphysics 9), for it is the end and completion of potency. (Aristotle, Metaphysics 9.8, 1049b4–1051a3; cf. Aquinas, Commentary on Metaphysics, bk. 9, lect. 7–9, nn. 1844–82.) But even in the order of generation and time, universally speaking act is prior to potency; for the potential is actualized by some actual being. But in one and the same thing, potency is prior to act; for something is first in potency and afterward becomes actual. Hence, his remark that knowledge is prior (that is, to thinking) in the order of generation in one and the same thing.

229. Therefore he concludes that, since the soul is act as knowledge, it is the first act of a natural body having life in potency. The Philosopher says the soul is “first act” not only to distinguish soul from the act that is activity, but also to distinguish it from the forms of the elements, for these always have their own activities, unless impeded.

230. Next, at however, such a body (412a28), he examines that part of the definition that has to do with the soul’s subject. And because the soul is the act of a natural body having life in potency, he also says that such is every organized body. And a body is called “organized” when it has a diversity of organs.

But diversity of organs is required in the body receiving life on account of the various activities of the soul. For the soul, which is the most perfect of the forms of bodily realities, is the principle of many different activities, so that it requires a diversity of organs in what is perfectible by it. But the forms of realities without soul, because of their imperfection, are the principles of few activities; hence, they do not need a diversity of organs in things perfectible by them.

231. Now, among souls, the soul of plants is found to be rather imperfect; this is why in plants there is less diversity of organs than there is in animals. Therefore to show that every body that admits life is organized, he takes his argument from plants, where there is less diversity of organs. So he says that even the parts of plants are diverse organs, but the parts of plants are very simple, that is, like to one another; for they lack the differentiation that we find in the parts of animals. Thus, the foot of an animal is made up of different parts, such as flesh, nerves, bones, and so forth, but the organized parts of plants do not have such a diversity of the parts from which they are composed.

232. And he manifests that the parts of plants are organized from the fact that diverse parts are for diverse activities. For example, a leaf functions as a covering for the pod, or fruit-bearing part, that is, for the part in which the fruit is born. The pod, again, protects the fruit itself. So, too, the roots have a function in a plant proportional to that of the mouth in an animal, because they draw in nourishment.

233. Next, at if, then (412b4), he gathers all these observations into one definition of the soul, saying that if some definition should cover every soul, it will be this: the soul is the first act of an organized natural body. He does not need to add “having life potentially,” for this is implied in “organized,” as is clear from what was said.

234. Then, at hence, it is unnecessary (412b6), he applies this definition to solve a difficulty. There had been much uncertainty about how one thing could come to be from the soul and body. Some had supposed a sort of medium uniting the two together by a sort of bond. But the difficulty can be set aside now that it has been shown that the soul is the form of the body. As he says, it is unnecessary to ask whether soul and body together make one thing any more than it is to ask the same about wax and the impression sealed on it, or about any other matter and its form. For, as is shown in Metaphysics 8, form is through itself united to matter as its actuality, and for matter to be united to form is the same as matter being in act. (Aristotle, Metaphysics 8.6, 1045a7–b23; cf. Aquinas, Commentary on Metaphysics, bk. 8, lect. 5, nn. 1755–67.) Moreover, although, as he goes on to say, being and one are predicated in many ways (in one way, of potential being, and in another way, of actual being), that is properly a being and a unity is act. For just as a potential being is not a being simply speaking but in a certain respect, so it is not one simply speaking but in a certain respect; for something is said to be one just as it is said to be a being. Therefore, just as the body has its being from the soul as from its form, so too, it is united to the soul immediately inasmuch as the soul is the body’s form; but insofar as it is its mover, there is no reason why it should not move it through something intermediate, insofar as one part is moved by the soul by means of another part.