Locke, Simplicity, and Extension

Abstract This paper aims to clarify Locke’s distinction between simple and complex ideas. I argue that Locke accepts what I call the “compositional criterion of simplicity.” According to this criterion, an idea is simple just in case it does not have another idea as a proper part. This criterion is prima facie inconsistent with Locke’s view that there are simple ideas of extension. This objection was presented to Locke by his French translator, Pierre Coste, on behalf of Jean Barbeyrac. Locke responded to Barbeyrac’s objection, but his response, along with a passage from Chapter XV of Book II of the Essay, “Of Duration and Expansion, considered together,” has been taken to show that he did not accept the compositional criterion. I examine these passages and argue that they are not in tension with but rather affirm that criterion.