Many theorists in epistemology and mind accept externalism with respect to content–namely, the claim that the conditions that individuate mental content are external to the occurrence of that content as a mental fact. Whatever it is that distinguishes a pain in the knee from a pain in the toe—or, alternatively, whatever it is that makes it possible for the subject to discriminate this pain as a pain in the knee from that pain as a pain in the toe—are factors and conditions located in the physical and external world. This much externalism seems to be required even if one is a thoroughly entrenched mentalist. This “content externalism” is captured, fairly effectively, by the more traditional distinction between concepts and percepts. What is then asserted by the mentalist is that concepts have their source or origin in the external world, but the perceptual content does not. Perceptual content can be identified in different ways which are: (1) the view that identifies the distinguishing feature of the perceptual with qualia, a position not far removed from the Lockean distinction between Primary and Secondary qualities; or, (2) the perceptual might also be characterized in terms of representationalism, where qualia are an essential part of the representational medium, but where the representational medium contains conceptual content as well. In either case, the perceptual is Type and/or Token distinct from whatever is the external physical conditions or states of affairs causally responsible for the occurrence of either the conceptual content or the perceptual content. An argument for the claim that percepts (colours, sounds, smells, touches, and so on) are essential and necessary is that, without such percepts, there can be no experience.