Speaking is so closely associated with making noises that such descriptions as ‘silent soliloquy’ and ‘soundless monologue’ have an air of paradox. Yet people frequently say things to themselves in such a way that not even a close observer has any reason to think they have done so. It is therefore tempting to suppose that on such occasions a sequence of surrogate speech sounds is produced in the person's head which he alone hears or introaudits, as if what distinguishes silent inner speech from normal speech is that the word substitutes are conveniently hidden from all save their producer.