This little book is not a text-book of psychology. It is exclusively concerned with one particular psychological problem, a problem, however, that stands at the very centre of psychology. The relations between mind and body are analysed; that is to say, the following three psychedelic problems are successively raised: What is the mind? What is the body? What are the relations between mind and body? But it is only the third problem which is extensively dealt with; the first two are only briefly defined.