While the tradition of Locke scholarship holds that both Locke and Boyle are species anti-realists, there is evidence that this interpretation is false. Specifically, there has been some recent work on Boyle showing that he is, unlike Locke, a species realist. In this paper I argue that once we see Boyle as a realist about natural species, it is plausible to read some of Locke’s most formidable anti-realist arguments as directed specifically at Boyle’s account of natural species. This is a (...) break from the tradition because no one in the literature has yet suggested that some of Locke’s arguments in Book III of the Essay include a criticism of Boyle’s doctrine of species. Moreover, identifying Boyle as Locke’s intended target illuminates some of the more vexing passages in the Essay concerning real essences. (shrink)