Nowhere within philosophy is it more difficult to draw lines of demarcation than in an attempt to isolate the philosophy of mind as a coherent subregion of the total philosophical terrain. The philosophy of mind grades off smoothly into questions of epistemology (the structure of sensory awareness and perceptual cognition), of ontology (the nature and multiplicity of substances), of the theory of action, of the philosophy of language and representation, of moral and social and political philosophy, and nowadays even into questions centered in the philosophy of science, in the theory of theories. In the case of Wilfrid Sellars, these difficulties are especially acute, for Sellars' philosophy of mind is intricately and inextricably woven into the fabric of a systematic philosophical vision of classical scope.