The Lagoon: How Aristotle Invented Science

by Armand Marie Leroi

‘actuality’ – entelekheia. It is this word, a bit of Aristotelian jargon, that is most distinctive about his theory of the soul. He often uses it in opposition to ‘potentiality’ – dynamis. The opposition runs deep into his physical theory. Any change, in Aristotle’s view, is the actualization of a potential. Thus when he says that the soul is an actuality, he’s stressing the fact that it’s something that previously existed only potentially; that it’s something that comes into being from something else. When combined with the claim that the soul of a living thing is ‘its form in its body’, it becomes clear that he means that the forms of unfertilized seed are mere potentials; and that those forms when realized in growing embryos and functioning adults are souls. This is still irritatingly abstract. But Aristotle tells us much about the properties of souls and they, in turn, tell us what he’s getting at. Some properties are quite general and apply to all that souls do in all creatures; others are more specific and apply just to humans.