The Nature of Human Beings

Aristotle follows Plato in trying to understand human beings as psychological beings, but he also tries to correct what he regards as Plato's mistakes.

For Aristotle, the question is what is the form of a human being. Human beings are natural bodies. 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 only in account.

So for Aristotle the form of a human being is a "soul" (ψυχή). The soul, according to Aristotle, is the "the cause (αἰτία) and starting-point (ἀρχὴ)" 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 one that Aristotle seems to have invented. It is a compound of three words: "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, however, is an end with qualification. Aristotle does not explain very clearly how living is an end with qualification, but the suggestion is that living is like what is the end without qualification. The end without qualification is not living. The end without qualification is the existence that characterizes the unmovable first mover.

So Aristotle's idea, in calling the soul a "first actuality," is the soul is the organization of the matter so that the matter constitutes a living natural body. In this way, the soul has an end. The end is living. In the case of a human soul, the end is living a human life. This end is an approximation of what is the end without qualification: the existence of the unmovable first mover.

(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).





Perseus Digital Library:
Aristotle, Metaphysics.
Henry George Liddell, Robert Scott, A Greek-English Lexicon:
ἐντελέχεια, entelecheia, noun, "full, complete reality,"
ὕλη, hylē, noun, "matter,"

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


"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.)