WHEN anyone starts to write on a subject, at which he has not hitherto worked professionally, his proper procedure should be to set out on a long course of reading, with careful preparatory annotations of all he has read. Such a course on a tremendous subject like the present one might easily take ten years. At the time when I determined to write this essay I was already over sixty-one, and it is safe to say that it would never have been written, if I had adopted this policy. Since I very much wanted to write it, the only alternative seemed to be to give up the idea of elaborate preparatory reading, and to make use from memory of a very considerable amount of unsystematic reading and thinking on the subject. A book written in this way can of course make no claim to the sort of authority that might be given to one which was based on exhaustive preliminary studies.
