Summary: On the Soul

Book I

All knowledge is admirable, yet some knowledge surpasses others, either for its precision or because it concerns objects of higher value and greater wonder ¹.

For these reasons, the study of the soul occupies a prominent place in the hierarchy of the sciences.

Moreover, the truths uncovered in this study benefit natural science, since the soul is, in essence, the principle of living beings ². Psychology is a branch of physics.

The aim of this work is to understand the nature and properties of the soul.

How is the soul to be characterised ontologically? Is it a substance, a quality, a quantity, or yet another category? Is it in potency or in act? Divisible or indivisible, without parts? Is the soul of a horse the same as that of a human, or does each species possess a distinct type of soul?

Is the soul immortal? Aristotle proposes an argument to approach the question: if the soul has a function of its own and remains independent of the body, it is immortal. If not, it cannot exist independently of the body.

Thought is the activity that appears distinctive to man; but if it is merely a form of imagination, it is inextricably bound to the body, since imagination presupposes sensation and, with it, the body.

All the soul's affections (its experiences) manifest through the body ³. Aristotle cites the examples of courage and gentleness. If so, then affections are forms embedded in matter and the study of the soul belongs to the physicist ⁴.

Psychological phenomena can thus be approached either as a dialectician or as a physicist, depending on whether one attends to the form or the matter of the affection in question. The dialectician, for example, will define anger as the desire for retribution, while the physicist will describe it as a boiling of the blood around the heart.

If there are properties of the soul independent of body and matter, they become the subject of the metaphysician's study.

As is his custom — as seen, for example, in The Physics — Aristotle begins by reviewing the history of doctrines on the soul advanced by his predecessors, from the pre-Socratics to Plato.

Most seem to agree on one point: the soul is animate. The animate, however, differs from the inanimate in two key respects: movement and sensation.

According to these philosophers, movement appears to belong to the soul, and many — Democritus, Leucippus, certain Pythagoreans, and Anaxagoras — assert that the soul is, above all and primarily, the mover ⁵. The soul moves things — first and foremost the body — and moves itself. This is why Democritus likened it to a kind of fire or heat ⁶, while Anaxagoras claimed that intelligence imparted motion to the universe ⁷.

Xenocrates, for his part, defined it as a number that moves itself ⁸, while Heraclitus asserted that it is precisely because the soul is movement that it can know things — which are in perpetual flux — for the moved is known by the moved.

However, this unanimity does not prevent Aristotle from criticising this theory. He categorically rejects the notion that movement can belong to the soul. For him, an animal consists of a mover — the soul, which is immobile — and the moved — the body.

Here, Aristotle expounds theories developed in another work, The Physics.

First, the mover is not necessarily itself moved: recall his famous definition of the agent intellect — which set the world in motion — as an unmoved mover.

Next, a mover may move either by itself or through something else — that is, accidentally, like sailors carried along by their ship.

Finally, he recalls the four species of motion identified in The Physics: translation, alteration, diminution, and increase.

None of these movements can belong to the soul. Each type of movement occurs in a place; therefore, if the soul were moved, it would have to occupy a place — something Aristotle deems impossible.

¹ On the Soul, I,1, 402a
² ibid.
³ ibid., 403a
⁴ ibid.
⁵ I,2, 403b
⁶ ibid., 404a
⁷ ibid., 405a
⁸ ibid., 404b