The Soul is the Form of the Body

⊕ "Substance is the cause of existing, and here, in living things, to exist is to live, and the soul is the cause and starting-point" (On the Soul II.4.415b).


On the Soul (in three books) is in the physical works. It is the first in a series of works devoted to living natural bodies.

I.1.             Introduction
I.2-5.         Previous views about the soul
II.1-3.       The soul is a substance and form
II.4.           Nutrition and reproduction
II.5-III.2.  Sense perception
III.3.          Imagination
III.4-8.       Intellect
III.9-11.     Movement of animals
III.12-13.   Summary

The Latin title of On the soul is De Anima. Every sensible substance has a nature as its "starting-point of change and staying unchanged." The nature is the organization of the material so that there is a substance of the kind.

These natures and organizations of materials are forms.

In the case of living things, Aristotle says that these forms are "souls" (ψυχαί).

The Soul in Living Sensible Substances

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"We say [in our ordinary way of talking] that his soul grieves, rejoices, is courageous, or afraid, and also grows angry, perceives and thinks; all these seem to be movements; hence one might suppose that [we are committed to thinking that] the soul is moved; but this is not a necessary inference. Let us grant that grief, joy and thinking are all movements, i.e., that each of them is a process of being moved; let us further admit that the movement is caused by the soul—e.g., that anger and fear are particular movements of the heart, and that thinking is a movement of this or of something else, some of these processes involving change of place and others change of quality in certain parts (of what parts and under what conditions need not be considered now): still to say that the soul gets angry is as if one were to say that it weaves or builds a house. [This sounds strange.] Probably it is better not to say that the soul pities, or learns, or thinks, but to say that it is the instrument whereby man does these things, that the movement does not take place in the soul, but sometimes penetrates to it, and sometimes starts from it" (On the Soul I.4.408b).
About the existence of the soul, Aristotle tries to correct the picture in Plato. In the Phaedo, Plato makes Socrates argue that the human soul has a life after death.

Aristotle does not have this understanding of the soul and its relation to the body.

For Aristotle, as the form of the body, the human soul is the organization of material so that there is a human being. Since this organization cannot exist without being the organization of some material, it does not continue to exist when a human being dies.

Aristotle also thinks that although a human being can become wise, what changes when his happens is not the soul. The soul is the starting-point that makes this change possible. As the form of the body, it is the organization of the material so that it is a living body with the potential to change in the various ways that characterizes members of the kind.

The Soul is a First Actuality

Aristotle says too that the soul is a "first actuality" (ἐντελέχεια ἡ πρώτη). ⊕

"Substances most of all are thought to be bodies, especially natural bodies, for they are the starting-points for other bodies. Of the natural bodies, some have life and some not. Life we say is self-nutrition and growth and decay, so every natural body having life is a substance as a composite. Since the body of a definite kind, viz., having life, it cannot be soul, for the body is not something predicated of a subject, but rather is itself to be regarded as a subject, i.e., as matter. So the soul must be substance as the form of a natural body, which potentially has life. And substance is actuality. The soul, then, is the actuality of a body. But is said in two ways, as knowledge and contemplating. The soul is an actuality like knowledge. Sleeping and waking presuppose the existence of soul, and waking corresponds to contemplation, sleeping to possession but not exercise since knowledge comes first. That is why the soul is the first actuality (ἐντελέχεια ἡ πρώτη) of a natural body having life potentially in it" (On the Soul II.1.412a).

Aristotle's discussion here is technical and confusing.

The word ἐντελέχεια does not occur in surviving texts before Aristotle. He seems to put it together from ἐντελής ("complete, full") and ἔχειν ("to have").

The soul as a first actuality is part of the theory of "substance" (οὐσία) Aristotle discusses in the Metaphysics.

We consider this theory in subsequent lectures.

The modifier "first" here is an instance of something we have seen before in Aristotle.

The forms of sensible substances are "separate from matter" but only with qualification. They are not separate from matter full stop. They are separate from matter "in account."

If we understand the modifier in "first actuality" along these same lines, the soul is an actuality but only with qualification. It is not an actuality full stop and without qualification.

Now we need to know what an actuality is and what qualification "first" imposes.

Actualities With and Without Qualification

Aristotle's idea is that a soul "actualizes" a potential for life. The potential is in the material, and the soul (as the organization of the material) is the "actualization" of this potential.

Consider an artifact, say a light switch, as an example.

The material (toggle, wires, and so on) has the potential to be a light switch, and the organization of the material as a light switch actualizes this potential. When the switch changes in position from off to on, the actualization and organization of the material does not change. The light switch remains a light switch throughout these changes.

These changes help us understand the qualification "first" imposes on actualities.

The actualization of the potential for material to be a light switch contains certain unrealized potentialities. The switch can be off or on, but it cannot be both at the same time.

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A human being is similar. He can be awake or sleep, but he cannot be both at the same time.

This, it seems, is what Aristotle has in mind when he says the soul is a first actuality. It is an actuality that contains unrealized potentialities and so is a "first" actuality.

This interpretation, if right, shows that Aristotle thinks that some forms are actualizations that contain no unrealized potentialities. We will think about them in a subsequent lecture.

The Teleological Conception

We turned to Aristotle's discussion of the soul because we wanted to understand how he explains the connection between specific behavior and the fact that it is beneficial.

To understand this takes some time, but we have made some progress.

Aristotle thinks that the human soul (because it is a form and organization of material) is a cause in the explanation of why human beings behave in the characteristic ways they do. One of these behaviors, as Aristotle understands human beings, is the acquisition of reason. Over time, as they mature from children into adults, Aristotle thinks that human beings naturally develop the cognition he calls reason. This, he thinks, makes them better.

It is thus an example of "nature act[ing] for something and because it is better" (Physics II.8.198b), but we still need to understand why the connection is not accidental.

According to the account in the Timaeus, the divine maker provides this explanation. Because reason is beneficial for human beings, the maker makes them so that they have reason.

Aristotle cannot avail himself of this sort of explanation because he replaces Plato's divine maker with the first unmoved mover, and this mover cannot make anything because it moves things without itself moving. (We try to understand this in subsequent lecture).

This means that we are still missing a crucial part of Aristotle's teleology.

To see this missing part, we need to look at Aristotle's Metaphysics. First, though, we are going to take a closer look at how he understands reason and how human beings acquire it.

Perseus Digital Library

Aristotle, Metaphysics.

Henry George Liddell, Robert Scott, A Greek-English Lexicon

ἐντελέχεια, entelecheia, noun, "full, complete reality"
ἐντελής, entelēs, adjective, "complete, full"
ὕλη, hylē, noun, "matter"

Arizona State University Library: Loeb Classical Library
Aristotle, On the Soul

"[Aristotle] thinks of [natural objects] as having a nature. A nature is a substantial form [a form that makes material be a substance, a human being for example]. In the case of an organism it is a soul. According to Aristotle it is this nature which explains the general pattern of behavior of an object of a certain kind. Indeed, Aristotle defines a nature as a principle of motion, or change, and rest. Given any particular change, for instance the growth to a given size of an organism, the change to this size will be accidental to the object, as this size is accidental to the object. But it is not accidental to grow to a size within the range of size objects this kind normally have. And the nature is supposed to explain why the object grows to this sort of size and then stops growing. And that it should behave like this is not accidental to it. Indeed for Aristotle, just as the nature or the soul is in some way the reality or actuality of the organism, so the life of the organism which exhibits this pattern of behaviour is the reality or actuality of this form, nature, or soul" (Michael Frede, "Introduction," 14. Aristotle's Metaphysics Lambda, 1-52).

"The forms of sensible substances involve potentiality in two ways, and hence are not pure actualities, though it is the essence of a form to be an actuality. They need matter to be realized in, and thus are the forms of objects subject to change. But, what is more, when we turn to the paradigms of sensible substances, living beings, it turns out that their forms themselves essentially contain an element of potentiality. When Aristotle in De Anima [On the Soul] II.1 defines the soul as the 'first actuality' of a certain kind of body, this very language reflects the fact that the soul in a way is constituted by the various abilities to exercise the life-functions characteristic of the kind of living being in question, but that not all these life-functions are exercised all the time. What is more, some of the abilities that characterize the soul, like virtue and knowledge, are only acquired. Thus, the forms of sensible substances are not pure actualities; they in part are constituted by unrealized possibilities and in that sense are not fully real. The form that is the unmoved mover, on the other hand, is pure actuality. It neither needs matter to be realized nor does it involve any abilities that might or might not be realized or exercised. The unmoved mover is just eternally thinking the same thought" (Michael Frede, "The Unity of General and Special Metaphysics: Aristotle's Conception of Metaphysics," 89-90).

"[I]t would seem that the forms of natural substances ... are separate only qualifiedly, namely, in account; and they are unchanging, but only qualifiedly. For though they do not come into being or pass away, they, unlike separate forms, do not exist eternally, but go in and out of existence instantaneously. And though they do not suffer change, they really are different at different times, as one can see in the case of human souls" (Michael Frede, "The Unity of General and Special Metaphysics: Aristotle's Conception of Metaphysics," 91. Essays in Ancient Philosophy, 81-95).

"[T]he forms at least of ensouled things [such as human beings] are not subject to change, at any rate, not in the sense in which Aristotle's natural philosophy approaches changeable objects, though they are principles of change and can have a very rich history, simply because the characteristic capacities of a living thing—which are what constitutes the soul, i.e., the form—can at various times be exercised or not exercised. If one sees something, it is not strictly speaking the soul which is undergoing some change but the living organism; nevertheless,the soul is a different soul, if one sees or has seen something" (Michael Frede, "Individuals in Aristotle," 69. Essays in Ancient Philosophy, 49-71).