Saul Kripke's 'Locke Lectures' were delivered in Oxford in 1973. Delivered in Kripke's usual extemporaneous style, for years the lectures have only been available as a transcription that has been informally exchanged among philosophers. This volume, which publishes the lectures, follows up on some of the themes on language that Kripke started to explore in his most famous work 'Naming and Necessity'.