The Nature of Human Beings
Aristotle follows Plato in trying to understand human beings as psychological beings, but he tries to correct what he regards as mistakes in Plato's theory of the existence of the human soul and its relation to the body. For Aristotle, human beings are natural bodies and as such have natures The nature of a natural body 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. Natures are forms. These forms are in matter and are separate only in account.
What, according to Aristotle, is the form of a human being? The answer is that this form is a "soul" (ψυχή). The soul, according to Aristotle, is the starting point for living.
"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 (συνθέτη). 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 (ὕλη). 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 (ἐπιστήμη) and contemplation (τὸ θεωρεῖν). The soul is 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).
The Soul is a First Actuality
In human beings, the soul is not an "actuality" without qualification. It is a "first actuality."
What does Aristotle mean by saying that the soul is a "first actuality"?
The word "actuality" (ἐντελέχεια) is a word that Aristotle seems to have invented. It is composed of "in" (ἐν), "end" (τέλοϛ), and "hold" (ἔχειν). In describing the soul as a "first actuality," Aristotle seems to mean that the soul is an "actuality" with qualification. The soul is the organization of material so that there exists an object that displays or "holds" some end. Living is this end. The soul is the starting point for living. Living is the end for the sake of which the material in the body has its organization. In this way, the soul "actualizes" the material.
The end the soul establishes as a first actuality is an end with qualification.
Aristotle does not explain very clearly how living is an end with qualification, but the suggestion seems to be that living is an imitation, or qualified form, of what is the end without qualification. The end strictly speaking and without qualification is not living. Rather, it is the perfect existence the unmovable first mover enjoys.
"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 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.)
How the human soul makes human beings like the unmovable first mover will become clearer in a subsequent lecture.
Two Platonic Mistakes
Plato thought that the reality of the human psychology consists in an object that can exist separately from the body. By conceiving of human beings as natural living bodies, and by conceiving of natural bodies as forms in matter, Aristotle tries to correct this Platonic conception of the soul and its relation to the body.
1. The soul is the form of the body. It is separate only in account.
Aristotle thought that Plato was wrong to think that the soul is an object that can exist independently of the body. The soul is not separate without qualification. As the form of a human being, the soul is in matter. It is the organization of the material so that there exist a living body. This organization is not separate without qualification. It is separate only in account.
2. The soul does not change. It is the
starting-point for change.
Aristotle thought that Plato was wrong to think that the soul can change and that, in particular, that it can become wiser and more like the pure state of contemplation it lost through incarnation. If the soul is the form of the living body, then it follows that the soul is not the kind of thing that can change. It is a human being that changes. It is the human being who can become wiser. In this, however, it is the human being, not the soul, that changes. The soul makes the change possible, but the soul itself does not change.
"We speak of the soul as being pained or pleased, being
bold or fearful, being angry, perceiving, thinking. All these
things are regarded as modes of movement, and hence it might
be inferred that the soul is moved. This, however, does not
follow. We may admit that being pained or pleased, or
thinking, are movements, and that the soul is the cause of
these movements. For example, we may regard anger or fear as
such and such movements of the heart.... Yet to say that the soul is angry is like saying that the
soul weaves or builds houses. Doubtless it is better to avoid
saying that the soul pities or learns or thinks, and to say
instead that the man does this with his soul (ἄνθρωπον τῇ ψυχῇ)" (On
the Soul I.4.408b1-15).