source

Aristotle expands his notion of happiness through an analysis of the human soul which structures and animates a living human organism. The parts of the soul are divided as follows:

The human soul has an irrational element which is shared with the animals, and a rational element which is distinctly human. The most primitive irrational element is the vegetative faculty which is responsible for nutrition and growth. An organism which does this well may be said to have a nutritional virtue.

The second tier of the soul is the appetitive faculty which is responsible for our emotions and desires (such as joy, grief, hope and fear). This faculty is both rational and irrational. It is irrational since even animals experience desires. However, it is also rational since humans have the distinct ability to control these desires with the help of reason. The human ability to properly control these desires is called moral virtue, and is the focus of morality. Aristotle notes that there is a purely rational part of the soul, the calculative, which is responsible for the human ability to contemplate, reason logically, and formulate scientific principles. The mastery of these abilities is called intellectual virtue.

Aristotle continues by making several general points about the nature of moral virtues (i.e. desire-regulating virtues). First, he argues that the ability to regulate our desires is not instinctive, but learned and is the outcome of both teaching and practice. Second, he notes that if we regulate our desires either too much or too little, then we create problems. As an analogy, Aristotle comments that, either “excess or deficiency of gymnastic exercise is fatal to strength.” Third, he argues that desire-regulating virtues are character traits, and are not to be understood as either emotions or mental faculties.

Degrees of soul

1. There is a nested hierarchy of soul functions or activities (413a23).
   1. Growth, nutrition, (reproduction)
   2. Locomotion, perception
   3. Intellect (= thought)
2. This gives us three corresponding degrees of soul:
   1. Nutritive soul (plants)
   2. Sensitive soul (all animals)
   3. Rational soul (human beings)
3. 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

1. 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)

2. Aristotle’s picture is not Cartesian (a dualism between soul and body):
   1. 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.
   2. 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.)
   3. 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.