Abstract

Descartes has standardly been read as holding that bodies achieve actual physical individuality through motion. He seems to say as much in Principles of Philosophy II, §25: “By ‘one body’ or ‘one piece of matter’ I mean whatever is transferred at a given time”. I contend, however, that this interpretation is quite wrong. Such a view would lead to an utterly untenable – and un-Cartesian – position whereby nothing could ever move, but nothing could be at rest either. Having noted this, I then examine §25 and related texts in some detail, and I argue that, as a matter of fact, they do not support this interpretation anyway. My conclusion is that physical individuality, for Descartes, has nothing to do with motion. Parts of matter at rest must be just as truly corporeal individuals as those that are moving, for Descartes treats the former as being just as physically efficacious as the latter. I contend that Descartes was happy to regard any conceivable region of extension as an actual body, regardless of whether it should happen to be moving or not.