Even to the undergraduate, plain thinking and plain living as the work of the past fifty years has made him, Professor Ryle's first book, long awaited, will seem one that he cannot afford not to possess and that he can afford to possess. This is a very considerable achievement on the part of both author and publisher. Not only is the book stimulating, enjoyable and original, but a quite unusually high percentage of it is true, the remainder at least false. In short, it stands head and shoulders above its contemporaries; it will deservedly enjoy a success, and even a vogue. Because this is so certain, and after emphasizing that it is to be welcomed most warmly as a voice which speaks, where too many are mute, for the genuine work being done at present in philosophy, the risk may be taken of referring freely to points of criticism.