In this book the insights derived from recent philosophy are used for the purpose of examining the theoretical foundations of operant psychology. The book first describes the philosophical tech-niques developed by Wittgenstein, Ryle, Austin, and others. It then goes on to show how, by the use of these techniques, the operant approach can usefully be regarded as a series of proposals for revising some of our main psychological concepts, and how disputes about different versions of behaviourism can be finally resolved. The book also includes a defence of a 'strong' version of operant psychology., a plea for total revision of the concept of punishment, and a detailed answer to the objection that an operant approach is in some way 'soulless' or inhumane. Skinner's views are sympathetically examined, and a new concept, that of an informative stimulus, is introduced in order to call attention to certain distinctive characteristics of human (as opposed to animal) behaviour.