The recasting is not difficult. _A self, in the psychological sense, is one of the particular psychological worlds._ It is not mind, but _a_ mind, the mental phenomena correlated with a particular nervous system, and arranged and determined in accordance with the tendencies of that system. We have made no mention of it hitherto, in this book, because our main business has been with general psychology, and we have had no need of it. Psychology, however, does not confine itself to the generalised world: and that is how it comes to be in different case from the physical sciences, and takes account, not only in self-defence, of the concept of self. If you go back to pp. 31 f., you will note that there is a =differential psychology=, a psychology of individual differences, as well as a general psychology. The variation of mental processes from observer to observer, and the limits and manner of this variation, are indeed just as much matter of observable fact, and therefore just as proper a subject for scientific enquiry, as their uniformity; and as the incidents of a man’s career may be set forth objectively, without praise or blame, in a biography, so may his psychological self, his mental processes in correlation with his nervous system, be set forth in a =psychography=. We ourselves, although we have been occupied with general psychology, and have for the most part spoken of ‘practised observers’ as a physicist might speak of ‘a sensitive galvanometer,’ without going into particulars,—we ourselves have, nevertheless, found frequent occasion to mention individual differences. The facts that we have thus touched upon incidentally are worked up, systematically, by differential psychology.