This volume is concerned with the philosophical foundations of Psychical Research. Traditional metaphysical theories have led to apparently insoluble problems concerning the nature of mind, of matter and the relation between the two. The author holds that these theories arise from misconception about the way in which words acquire meaning. His aim is to show that once the relation between words and the experienceable entities which they mean is clearly understood, these seemingly insoluble problems disappear, and the metaphysical theories which give rise to them are seen to be literally nonsensical. The philosophy which results is a radically empirical one, a form of Neutral Monism. The book intended to 'clear the decks' for Psychical Research by removing certain traditional pseudo-problems, but it will be of interest to all who followed the revival of Empiricist Philosophy, whether they are students of Psychical Research or not. It is written in a pithy and sparkling style, with a minimum of technical terms, and serves as an introduction to Empiricist Philosophy. Originally published 1949.