A great deal of the criticism directed at John Locke's theory of abstract ideas, including George Berkeley's famous critique (PHK, Intro § §7-21), 1 assumes that a Lockean abstract idea is a special kind of idea which by its very nature either represents many diverse particulars or represents separately things that cannot exist in separation (see PHK, Intro §10). 2 I will call this the intrinsic theory of abstraction, since it holds that abstract ideas differ intrinsically from concrete (i.e., non-abstract) ideas.The claim that Locke held the intrinsic theory has been challenged by scholars such as Kenneth Winkler and Michael Ayers who regard it as uncharitable to Locke in light of the obvious problems faced by this theory of abstraction. Winkler and Ayers argue that Locke held instead that to have an abstract idea is to attend selectively to some portion of the content of a particular idea. On this view, to have an abstract idea is not to have a special kind of idea but to have an ordinary idea in a special way. I will call this the extrinsic theory of abstraction, since it holds that ideas are not intrinsically abstract but rather are abstract in virtue of the manner in which they are had (perceived). According to Ayers, this interpretation is contextually plausible since Locke was greatly influenced by Antoine Arnauld, and Arnauld endorsed the extrinsic theory of abstraction.I argue, on the contrary, that both Arnauld and Locke endorse the intrinsic theory. I begin, in §1, with a more careful definition of the difference between the intrinsic and extrinsic theories of abstraction. In §2 I show that, despite Arnauld's talk about selective attention, Arnauld holds the intrinsic theory. In §3, I show that a consistent interpretation of Locke's remarks on abstract ideas can be developed on the assumption that Locke did indeed follow Arnauld in this. Thus, contrary to Winkler and Ayers, both textual and contextual evidence favors the attribution of the intrinsic theory to Locke. In §4, I address the argument from interpretive charity against the attribution of the intrinsic theory to * Forthcoming in British Journal for the History of Philosophy.