Copyright © 2008, S. Marc Cohen 1 Revised 3/4/08
Aristotle on the Soul
Matter and Form
Aristotle uses his familiar matter/form distinction to answer the question
“What is soul?” At the beginning of De Anima II.1, he says that there are three sorts of substance:
- Matter (which is a dunamis: potentiality)
- Form (which is an entelecheia: actuality)
- The compound of matter and form
Aristotle is interested in compounds that are alive. These—plants and
animals—are the things that have souls.
What makes something a living thing? That is, what is the formal cause of it
being alive? Aristotle seems to give two answers:
- “By ‘life’ I mean self-nourishment, growth, and decay” (412a14).
- It is the soul that makes something alive.
The idea seems to be that self-nourishment, etc., are the characteristic signs by
which we identify the presence of life, whereas soul is that which explains the
presence of those features.
Since form is what makes matter a “this,” the soul is substance in the sense of
the form (412a20) or essence (412b12) of a living thing. Here is Aristotle’s
first answer to the question of what the soul is (412a20):
The soul, then, must be substance as the form of a natural body that is
Note that ‘form’ here does not mean shape, but rather actuality (412a21):
Now substance is actuality; hence the soul will be the actuality of this
specific sort of body.
So the soul is the actuality of a natural body that is potentially alive.
Grades of Actuality and Potentiality
Recall the grades or levels of potentiality and actuality. To say that the soul is
an actuality (entelecheia) means it is either a first or a second actuality.
Aristotle tells us that the soul is: a first actuality (412a27):
The soul is the first actuality of a natural body that is potentially alive.
Recall that a first actuality is a kind of potentiality—a capacity to engage in
the activity which is the corresponding second actuality. The second actuality
is the exercise of a function (ergon); the first actuality is the capacity or
disposition to exercise that function. So soul is a capacity—but a capacity to do
A living thing’s soul is its capacity to engage in the activities that are
characteristic of living things of its natural kind and conducive to their
well being and survival. What are those activities? Some are listed in DA II.1;
others in DA II.2 (in increasing order of degree or complexity):
- Movement and rest (in respect of place)
So anything that nourishes itself, that grows, decays, moves about (on its own,
not just when moved by something else), perceives, or thinks is alive. And the
capacities of a thing in virtue of which it does these things constitute its soul.
The soul is what is causally responsible for the animate behavior (the life
activities) of a living thing.
Degrees of soul
There is a nested hierarchy of soul functions or activities (413a23).
- Growth, nutrition, (reproduction)
- Locomotion, perception
- Intellect (= thought)
This gives us three corresponding degrees of soul:
- Nutritive soul (plants)
- Sensitive soul (all animals)
- Rational soul (human beings)
These are nested in the sense that anything that has a higher degree of soul
also has all of the lower degrees. All living things grow, nourish themselves,
and reproduce. Animals not only do that, but move and perceive. Humans do
all of the above and reason, as well. There are further subdivisions (listed in
DA II.3) within the various levels, which we will ignore. (E.g., all animals
perceive, but some have only the sense of touch, others have several senses,
others have all five senses.)
Soul and Body
Does Aristotle have an answer to the mind-body problem? This is a question
that has vexed (and divided) interpreters of Aristotle in recent years. Almost
(but not quite) everyone agrees that he is not a dualist, but he does not seems to
be a crude physicalist, either. (That is, he does not think that mental states are
brain states—or heart states—or bodily processes at all.) Some think that he is
a proto-functionalist. But the prevailing opinion seems to be that he does not
really address that Cartesian question, mainly because his conception of the
body is so different from Descartes’ mechanical conception.
Still, he does say things about some issues that are clearly related to the mindbody
A key question for the ancient Greeks (as it still is for many people today) is
whether the soul can exist independently of the body. (Anyone who believes in
personal immortality is committed to the independent existence of the soul.)
Plato (as the Phaedo makes clear) certainly thought that the soul could exist
separately. Here is what Aristotle has to say on this topic (414a20ff):
…the soul is not a body but requires a body; for it is not a body, but it
belongs to a body, and for that reason it is present in a body, and in
this sort of body.
So on Aristotle’s account, although the soul is not a material object, it is
not separable from the body. (When it comes to the intellect, however,
Aristotle waffles. See DA III.4)
The soul is the cause (aition) of life (“the soul is the cause and principle of the
living body,” 415b8). That is, the soul plays an explanatory role:
- Living is defined in terms of characteristic activity: (some or all of)
growth, nutrition, locomotion, sensation, thought (413a23).
- Substance is the cause of being, and for living things, being = living
Hence Aristotle thinks that his definition immediately gives us an answer to a
basic question about the relation between soul and body, a question that is
analogous to one that is sometimes raised in contemporary discussions of the
mind-body problem. The question is whether the soul and the body “are one”:
Hence we need not ask whether the soul and body are one, any more
than we need to ask this about the wax and the seal or, in general,
about the matter and the thing of which it is the matter. For while one
and being one are spoken of in several ways, the actuality <and what
it actualizes> are fully one. (412b6-9)
Unfortunately, it is not quite clear just what the answer is. Why should we not
ask the question? Is it because the answer is obvious? If so, is the answer
“obviously yes” or “obviously no”? One might go either way here:
- Obviously yes: soul is form (or actuality), and body is matter (or what
gets actualized). So if “actuality <and what it actualizes> are fully
one,” that means that soul and body are fully one. So we needn’t ask
whether soul and body are one because they obviously are.
- Obviously no: the wax and the seal are clearly not identical, so they
are not one. So if body and soul are like wax and seal, then we needn’t
ask whether soul and body are one because they obviously are not.
A better solution is to say that the reason we shouldn’t ask is that it’s obvious
that the answer is “in a way yes, and in a way no.” We don’t need to ask about
the wax and the seal because it’s obvious in what sense they are one, and in
what sense they are not one. The wax and the seal (that appears in it) are not
two separable things, but we can distinguish them in thought. The seal is the
shape that is imprinted in the wax and makes it the kind of waxen thing it is.
So they are one in that they are inseparable, and they are not two substances,
one inhering in the other. But the sense in which soul and body are one does
not make the soul a body, or a kind of body.
Aristotle vs. Descartes
Aristotle’s picture is therefore not Cartesian:
- There is no inner/outer contrast. The soul is not an inner spectator, in
direct contact only with its own perceptions and other psychic states,
having to infer the existence of a body and an “external” world.
There is thus no notion of the privacy of experience, the incorrigibility
of the mental, etc., in Aristotle’s picture.
- The soul is not an independently existing substance. It is linked to the
body more directly: it is the form of the body, not a separate substance
inside another substance (a body) of a different kind. It is a capacity,
not the thing that has the capacity.
It is thus not a separable soul. (It is, at most, pure thought, devoid of
personality, that is separable from the body on Aristotle’s account.)
- Soul has little to do with personal identity and individuality. There is
no reason to think that one (human) soul is in any important respect
different from any other (human) soul. The form of one human being is
the same as the form of any other.
There is, in this sense, only soul, and not souls. You and I have
different souls because we are different people. But we are different
human beings because we are different compounds of form and matter.
That is, different bodies both animated by the same set of capacities, by
the same (kind of) soul.
[This last point, of course, is controversial. Those who believe in
individual essences in the Metaphysics will surely invoke them here in
an attempt to make individual souls the true animate individuals—the
bearers of psychological predicates.]