“No man can see farther into a generalization than his knowledge of detail extends.” That saying of William James is true of all the branches of science; but it has a special value for students of social philosophy. Social life is so obviously a matter of personal experience that an academic Robinson Crusoe may easily be less competent in his knowledge of detail than a business man, if the business man thinks at all. This is not a compliment to the business man, nor an insult to the academic scholar; for the majority of those who deal with practical issues seem to be far more incompetent than the majority of scholars. But it is essential for social philosophy that practical experience of some kind should be used. Indeed, just as a student of chemistry nowadays depends at every step upon experiment, so a student of social life should take care to play a part in some form of active social life, whether as directing, co-operating, or obeying. One cannot get chemistry out of books; still less can one find social philosophy there. Therefore the number of books written or read is no criterion of the vigour of social philosophy in any generation—it is so easy to write books about other books, and so easy to read the same material many times.