This was Foulkes’ membership paper to the British Psycho-Analytical Society and his major theoretical paper on psychoanalysis. His comprehensive review of the literature to that time, both of the classical continental authors, particularly Ferenczi who introduced the term introjeetion into psychoanalysis, and of more recent British analysts, focuses on problems of terminology. He underlines the danger of talking about the same things in different words, or of different things in the same words, and he proposes some alterations in the definition and usage of the terms ‘identification’, ‘projection’ and ‘introjeetion’ in particular.