Christopher Peacocke has presented an original version of the perennial philosophical thesis that we can gain substantive metaphysical and epistemological insight from an analysis of our concepts. Peacocke's innovation is to look at how concepts are individuated by their possession conditions, which he believes can be specified in terms of conditions in which certain propositions containing those concepts are accepted. The ability to provide such insight is one of Peacocke's major arguments for his theory of concepts. I will critically examine this “fruitfulness” argument by looking at one philosophical problem Peacocke uses his theory to solve and treats in depth.

Peacocke (1999, 2001) defines what he calls the “Integration Challenge.” The challenge is to integrate our metaphysics with our epistemology by showing that they are mutually acceptable. Peacocke's key conclusion is that the Integration Challenge can be met for “epistemically individuated concepts.”A good theory of content, he believes, will close the apparent gap between an account of truth for any given subject matter and an overall account of knowledge. I shall argue that there are no epistemically individuated concepts, and shall critically analyze Peacocke's arguments for their existence. I will suggest more generally that the possession conditions of concepts and their principles of individuation shed little light on the epistemology or metaphysics of things other than concepts. My broader goal is to shed light on what concepts are by showing that they are more fundamental than the sorts of cognitive and epistemic factors a leading theory uses to define them.1