Reports of people’s thoughts and feelings relate to occurrences of a special category – mental acts. This book discusses the concepts used in such reports. Originally published in 1957 and with a new preface in 1971, this book is now a classic in the philosophy of psychology.

It begins with a general discussion of concepts, as specific abilities exercised in acts of judgment, and of their formation. The author here attacks the doctrine of Abstractionism, that concepts are formed and exercised by noticing recurrent features in experience. This doctrine, which is taken for granted in many philosophical and psychological works, including contemporary ones at the time, is in the author’s view not really adequate to account for any concept whatever, and is specially inadequate as regards psychological concepts. These concepts, he suggests, are irreducibly analogical developments of concepts whose primary application is to sensible objects; the suggestion is worked out in detail for the concepts ‘thought’ and ‘sensation’. Among the topics discussed in the course of the argument are Russell’s theory of judgment, the reference of thoughts to definite individual objects, Descartes’ ‘Cogito’, and the possibility of attributing experiences otherwise than to a living organism.

The author’s later thoughts on some of the questions discussed are briefly indicated in the 1971 preface.

Peter Geach (1916–2013) was a British philosopher. He was Professor of Logic at the University of Leeds (1966–1981) and subsequently professor Emeritus. He was admired for his mastery of logic and work on ethics.