Enneads IV.3: Psychological Questions
The Soul Present in the Body as Light in Air
22. This is the better illustration: the soul is present in the body as light is present in air. Light is indeed present in air without being present to it; that is, light is present to the whole air without mingling with it, and light remains within itself while the air escapes. When the air, within which light radiates, withdraws from the light, the air keeps none of the light; but it is illuminated so long as the air remains subject to the action of light. Air, therefore, is in light, rather than light is in air. While explaining the generation of the universe, therefore, Plato properly locates the body (of the world) in the soul, and not the soul in the body. He also states that there is a part of the soul that contains the body, and another in which there is no body, in this sense, that there are soul-powers of which the body has no need. The case is similar with the other souls. Their powers in general are not present to bodies, and only those powers of which the body stands in need are present to it. These however are present to the body without being built up either on the members, or upon the body as a whole. For sensation, the faculty of feeling is entirely present to the whole organ which is feeling (as, for instance, to the whole brain); likewise for the other functions, the different faculties are each present to a different organ. I shall explain myself.
WHILE THE SOUL-POWER IS EVERYWHERE, THE PRINCIPLE OF ACTION IS LOCALIZED IN THE SPECIAL ORGAN.
23. Since, for the body, being animated amounts to being penetrated by the light shed by the soul, every part of the body participates therein in some particular manner. Each organ, according to its fitness, receives the power suitable to the function it fulfils. Thus we may say that the power of sight resides in the eyes; that of hearing in the ears; that of taste in the tongue; that of smell in the nose; that of touch in the whole body, since, for the latter sense, the whole body is the organ of the soul. Now as the instruments for touch are the first nerves, which also possess the power of moving the organism, as they are the seat of this power; as, besides, the nerves originate in the brain, in the brain has been localized the principle of sensation and appetite—in short, the principle of the whole organism; no doubt because it was thought that the power which uses the organs is present in that part of the body where are the origins of these organs. It would have been better to say that it is the action of the power that makes use of the organs that originates in the brain; for that part of the body from which starts the movement impressed on the organ had to serve somewhat as a foundation for the power of the workman, a power whose nature is in harmony with that of the organ (it sets in motion); or rather, this part of the body does not serve as foundation for this power, for this power is everywhere, but the principle of the action is in that part of the body in which is the very principle of that organ.
REASON IS IN THE HEAD, BUT NOT IN THE BRAIN, WHICH IS THE SEAT OF THE INTERMEDIARY, THE POWER OF SENSATION.
On the other hand, as the power of sensation and the power of appetite, which belong to the sensible and imaginative soul, are beneath reason, because they are related to what is inferior, while reason is above, the result was that the ancients localized reason in the highest part of the animal, in the head; not that reason is in the brain, but because reason is seated in the sense-power, by the intermediation of which, only, reason may be said to reside in the brain. The sense-power, surely, had to be attributed to the body, and, within the body, to the organs most capable of lending themselves to its action. Reason, which has no (direct) dealing with the body, had however to be in relation with the sense-power, which is a form of the soul, and can participate in reason. The sense-power, does, to a certain extent, judge; and the power of imagination has something intellectual. Last, the appetite, and the desire somehow connect with imagination and reason. Reason, therefore, is in the head, not as in a locality, but because it is in relation with the sense-power which resides in that organ, as has been shown above.