ABSTRACT
David Hume’s discussion of personal identity is preceded by a section concerning the immateriality of the soul. Hume has in mind a philosopher who maintains that substance itself must be utterly different from any of its qualities, modes, or acts. Hume completes his critique of the idea of a mental substance by rejecting a definitional trick. If substance is defined as “something which may exist by itself,” then every impression or idea will itself be a substance, for every impression and idea is itself a distinct existence. With the main argument in hand, Hume turns to the supposed simplicity of the soul. He considers a proposed refutation of materialist conceptions of the soul that runs as follows. If the soul is an extended thing, then it will have parts, a top and a bottom, a left side and a right side.
