What Living Natural Bodies Are

The Soul is the Substance as the Form

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

"The soul of living things is the substance which accords with the account, i.e., the form and what it is to be such a body" (Metaphysics VII.1035b).


Outline of On the Soul (the first in a series of physical 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
All natural bodies have natures. The nature is the "starting-point of change and staying unchanged." It is the organization of the material so that there exists a body of the kind. These natures are forms, and these forms are in matter and separate in account.

In the case of living natural bodies, Aristotle says that the form is a "soul" (ψυχή).

The Soul in Living Natural Bodies




"We say that the 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 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. 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).
By conceiving of human beings as natural living bodies, and by conceiving of natural bodies as forms in matter, Aristotle tries to correct what he understands as Plato's mistakes.

Plato thought the soul exists separately from the existence of the body. Aristotle thinks this is a mistake. As the form of a natural body, the soul is in matter and separate only with qualification. It is an organization of material so that there exists a living body.

Plato thought the soul can change and can be in a better or worse state, and Aristotle thinks this is a mistake too. Because the soul is the organization of the material into a living natural body, it is not the kind of thing that can change in this way. A human being can change. A human being can become wiser, for example. In this, however, it is the human being, not the soul, that changes. The soul makes the change possible. It is the starting-point for the ways living natural bodies change, but the soul itself does not change when the body changes in these ways.

The Soul is a First Actuality



ἐντελέχεια ("actuality") is a noun Aristotle invents by combining ἐντελής and ἔχειν. The adjective ἐντελής means "complete, full." The infinitive ἔχειν means "to have" or "to hold." A first actuality is an actuality but is an actuality with qualification. The qualification is "first." It qualifies the way the existence is "complete, full."

"Substances (οὐσίαι) 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 do not. Life we say is self-nutrition and growth and decay. Thus every natural body having life is a substance as a composite. But since it is a body of a definite kind, viz., having life, the body 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 (ψυχὴν οὐσίαν εἶναι ὡς εἶδος) of a natural body, which potentially has life. And substance is actuality (ἐντελέχεια). The soul, then, is the actuality of a body. But actuality is of two kinds, corresponding to knowledge and contemplation. The soul is an actuality like knowledge. Sleeping and waking presuppose the existence of soul, and waking corresponds to contemplation, sleeping to knowledge since it 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 conceives of the soul as the "first actuality" (ἐντελέχεια ἡ πρώτη) of the body.

The distinction between an actuality with and without and qualification is difficult. It will become a little clearer in subsequent lectures. The discussion here is a first sketch.

As the form of a living natural body, the soul is the organization that makes material constitute a living natural body. Because the material has this organization, there is a natural body that lives in the way that characterizes members of the kind. Without the organization, there is no natural body and hence no characteristic way life. There is only a heap of materials that have the potential to be a living natural body. The soul is the "actuality" of this potential.

Consider a human being. If to be a human being is to be a rational animal, then the soul of a human being is the organization of the material so that it has the form of a rational animal. Each human being lives a human life because each is material organized as a rational animal. Without this organization, there is no human being. There is only material with the potential to be a human being. The soul of a human being is thus the actuality of this potential.

This makes it a little clearer what it is for the soul to be an "actuality," but it remains to know why Aristotle thinks it is a "first actuality" and hence is an actuality with qualification.

The answer, it seems, in the case of a human being, is that living consists in different activities at different times. Human beings grow and mature, eat in certain circumstances, and sleep in others. As the organization of the material, the soul explains the existence of the potentials to engage in these activities. So the soul of a human being is a "first" actuality.

In contrast, an actuality without qualification is the form of an existence that is not different at different times. Something with this existence has a "complete, full" existence without qualification. It does not have potentials it exercises in different circumstances.

Aristotle thinks some things have a "complete, full" existence without qualification. This will become a little clearer when we turn to Aristotle's metaphysics in a subsequent lecture.




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. 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).


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