Aristotle’s On the Soul defines soul as that which makes actual a natural body (as opposed to a man-made body) that potentially has life. Without it, the body isn’t alive and, in fact, slowly quits being a body. The soul is the form of which body is the matter.
OK, that only makes so much sense to me, especially when Aristotle starts saying that part of the soul is immortal and can live without a body. What’s more interesting to me in On the Soul, today at any rate, is the Philosopher’s orders of living beings. According to Aristotle, soul has several powers or faculties: nutritive powers, sensitive powers, and calculating powers. They come in that order, and no living thing can have the second category of powers without the first, or the third without the second. All living things have nutritive powers (which he sometimes calls the nutritive soul). They consume food to grow, maintain their bodies, and reproduce. And that’s as far as plants go. Animals, on the other hand, have sensitive powers in addition to nutritive power. Some animals have only the sense of touch. Some also have hearing or smell. Some have all five. But humans have reasoning powers in addition to all those. Aristotle sometimes calls these human reasoning powers “psychic” powers (psychikos in Greek).
Interestingly, in I Corinthians, Paul uses Aristotle’s term, psychikos, and contrasts to it yet one more order of earthly life: the pneumatikos, the spiritual. I love to see that a Biblical author used the pagan philosopher’s ideas and didn’t so much refute them as simply add to them. Because Aristotle is fascinating even when he’s wrong. For instance, in going over the sensitive powers, he argues extensively that sight must have a transparent medium: either air or water. A white card doesn’t appear white when placed right against the eye, he points out. Yet how can it affect the eye at a distance? The color must set in motion the air right next to it, which in turn sets our eye in motion. If “interspace” were a vacuum, he speculates, we would not be able to see the stars on the vault of heaven. I wanted to shake my head and chuckle at his mistaken logic and silly thinking until I read him say in the next paragraph that sound works exactly the same way. Not so silly after all. With regard to sound, 2500 years of science have supported Aristotle’s view. Movie history supports him, too. In space no one can hear you scream.