Wilfrid Sellars (1912–89) has been called the most profound and systematic epistemological thinker of the twentieth century. Many of his ideas have become widely acknowledged, including his attack on the "myth of the given", his functionalist treatment of intentional states, his proposal that psychological concepts are like theoretical concepts, and his suggestion that attributions of knowledge locate the knower "in the logical space of reasons". This clear, comprehensive and authoritative work will become the standard point of reference for all philosophers seeking to understand Sellars's hugely significant body of work.