This book comes from a course of lectures first given in Cambridge in the Easter Term of 1972 and repeated, in a revised and augmented form, in Michaelmas 1973. Quite a lot of people came, ranging from freshmen to graduate students and faculty. Many of them had found themselves dissatisfied with recent linguistic philosophy, and yet knew that in some way language has deeply mattered to philosophy. I tried to describe, in a few case studies, some remarkable ways in which language has mattered, and then speculated on why this should have been so. The approach was often more historical than the audience expected, but to understand why language mattered we had to think not only how it has mattered but also when it has mattered. None of us was concerned with boring and ephemeral questions such as whether linguistic analysis is worthy or iniquitous. We were trying to understand the structure of something very striking about philosophical speculation. I hope that students elsewhere with doubts and fascinations similar to ours may find this book helpful.