In this lecture, I want to convey some ideas about linguistic communication which will probably be found not only unfamiliar, but also difficult to grasp at a first encounter. Perhaps I am being too ambitious in so short a compass. At any rate, my only hope of success is to work within closely defined limits, to concentrate more upon expounding these suggestions than upon detailed justification of them, and to say as little as possible about the shortcomings of alternative proposals which are current. The references which I cite have also been rather narrowly selected. As to the limits of this discussion, it will be confined to linguistic communication, as effected by the use of sentences. This is not to deny that there are non-linguistic forms of communication, both between men and between other animals, nor that there are other units of linguistic communication than the sentence; I have taken only what seems most typical of human communication, in order to make the task manageable.