Thales raises a lodestone over a small piece of iron.

Why a magnet raises a question about the soul

Aristotle (384–322 BCE), the Greek philosopher from Stagira, preserves a remark about his predecessor Thales of Miletus. A piece of lodestone can lie quite still on a table. Bring a small piece of iron close to it and the iron moves towards the stone. Where does that movement begin? The observer’s hand need never touch the iron. It is precisely this separation between the moving thing and what moves it that makes the little experiment worth a philosopher’s attention.

A stone moves something else

Thales also, according to the traditional stories of him, appears to have conceived of the soul as a sort of kinetic principle, if it be true that he said the loadstone has a soul because it moves iron.

– Aristotle, On the Soul, 1902, p. 15.[1]

In his work on the soul, Aristotle asks what earlier thinkers took as evidence of life. One capacity that recurs in their accounts is that of setting something in motion. The magnet supplies an unusual test. A horse draws a cart by moving its own body. The stone takes no step and makes no visible effort. Yet something quite unmistakable happens near it. An observer attending chiefly to this effect might reasonably wonder whether a principle of movement also belongs to this apparently idle piece of matter.

What kind of testimony survives?

Aristotle is reporting what people say about Thales and cautiously inferring a view from the story. We do not possess the words of Thales himself here. The distinction matters because a judgment intervenes between the moving piece of iron and the word soul. Anyone can pick up the iron and repeat the observation. What the experiment establishes about the nature of a living thing is the question Aristotle leaves open for discussion.