C. I. Lewis’s version of pragmatism, which he called “conceptualistic pragmatism,” has been little studied and is nowadays overlooked, eclipsed by the more famous pragmatisms of Dewey and James. However, it was Lewis’s version that came to dominate the formation of post-1945 pragmatism in the United States. It provided the framework in which Quine (his former student), Sellars, Davidson, Rorty and Brandom operated. Roughly, that structure involved a passive, sensory ineffable given and an ordering and classification of the given by a priori categories. Comprehending those categories was a matter of apprehending a priori truths, but those categories were also changeable. Rational change involved giving some up and substituting others to meet...