 Many philosophers hold that beliefs and concepts are related in the following way: in order to have a belief that x is F, for any object x and any property F, a subject must have concepts of the object and the property, and must deploy those concepts in the belief. When concepts and beliefs are related in this way, belief content is said to be conceptual. Call this view belief conceptualism (endorsed by Dretske 1981 and Martin 1992a, among others). Belief conceptualism is typically defended on the grounds that beliefs differ from one another according to which concepts one has. One can believe that whales swim without believing that large sea-dwelling mammals swim, even though whales are large sea-dwelling mammals. According to a common defense of belief conceptualism, the relevant beliefs differ in which concepts the thinker is deploying, and that explains how it is that someone can have one of these beliefs without the other. According to a related defense of belief conceptualism, it explains why some thinkers cannot have any thoughts about some subject matter. Suppose the thinker lacked the concept ‘whale’: she had no idea what whales were, nor even that there was such a thing. Arguably such a thinker could not believe that whales swim, that whales are blue, or anything else about whales. According to belief conceptualism, this is because she lacks the concept of a whale. A full specification of belief conceptualism would require explicating what concepts are, and what it is to possess and deploy one.