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:
The compound of matter and form
Aristotle is interested in compounds that are alive. These – plants and animals – are the things that have souls. Their souls are what make them living things.
Since form is what makes matter a ?this,? the soul is the form of a living thing. (Not its shape, but its actuality, that in virtue of which it is the kind of living thing that it is.)
Grades of Actuality and Potentiality
Aristotle distinguishes between two levels of actuality (entelecheia). At 412a11 he gives knowing and attending as examples of these two kinds of actuality. (It has become traditional to call these first and second actuality, respectively.) At 412a22-26 he elaborates this example and adds this one: being asleep vs. being awake. But he does not fully clarify this important distinction until II.5 (417a22-30), to which we now turn.
At 417a20, Aristotle says that there are different types of both potentiality and actuality. His example concerns different ways in which someone might be described as a knower. One might be called a knower in the sense that he or she:
is a human being.
has grammatical knowledge.
is attending to something.
A knower in sense (a) is someone with a mere potential to know something, but no actual knowledge. (Not everything has this potential, of course. E.g., a rock or an earthworm has no such potential.) A knower in sense (b) has some actual knowledge (for example, she may know that it is ungrammatical to say ?with John and I?), even though she is not actually thinking about it right now. A knower in sense (c) is actually exercising her knowledge (for example, she thinks ?that?s ungrammatical? when she hears someone say ?with John and I?).
Note that (b) involves both actuality and potentiality. The knower in sense (b) actually knows something, but that actual knowledge is itself just a potentiality to think certain thoughts or perform certain actions. So we can describe our three knowers this way:
Second potentiality = first actuality
Here is another example (not Aristotle?s) that might help clarify the distinction.
First potentiality: a child who does not speak French.
Second potentiality (first actuality): a (silent) adult who speaks French.
Second actuality: an adult speaking (or actively understanding) French.
A child (unlike a rock or an earthworm) can (learn to) speak French. A Frenchman (unlike a Frech infant, and unlike most Americans) can actually speak French, even though he is silent at the moment. Someone who is actually speaking French is, of course, the paradigm case of a French speaker.
Aristotle uses the notion of first actuality in his definition of the soul (412a27):
The soul is the first actuality of a natural body that is potentially alive.
Remember that first actuality is a kind of potentiality -a capacity to engage in the activity which is the corresponding second actuality. So soul is a capacity – but a capacity to do what?
A living thing?s soul is its capacity to engage in the activities that are characteristic of living things of its natural kind. What are those activities? Some are listed in DA II.1; others in DA II.2:
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)
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 within the various levels, which we will ignore.)
Soul and Body
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 we know from the Phaedo) certainly thought that the soul could exist separately. Here is what Aristotle has to say on this topic:
. . . the soul does not exist without a body and yet is not itself a kind of body. For it is not a body, but something which belongs to a body, and for this reason exists in a body, and in a body of such-and-such a kind (414a20ff).
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)
Aristotle?s picture is 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.