It is impossible to discuss the different theories in detail here, but I will briefly summarise the more important points, (1) Hypnotism, as a science, rests on the recognition of the subjective nature of its phenomena. (2) The theories of Charcot and the Salpetriere school are practically a reproduction of mesmeric error. (3) Liebeault and his followers combated the views of the Salpetriere school and successfully substituted their own, of which the following are the important points: (_a_) Hypnosis is a physiological condition, which can be induced in the healthy. (_b_) In everyone there is a tendency to respond to suggestion, but in hypnosis this condition is artificially increased. (_c_) Suggestion explains all. Despite the fact that the members of the Nancy school regard the condition as purely physiological and simply an exaggeration of the normal, they consider it, in its profound stages at all events, a form of automatism. These and other views of the Nancy school have been questioned by several observers. As Myers justly pointed out, although suggestion is the artifice used to excite the phenomena, it does not create the condition on which they depend. The peculiar state which enables the phenomena to be evoked is the essential thing, not the signal which precedes their appearance. Within recent times another theory has arisen, which, instead of explaining hypnotism by the arrested action of some of the brain centres which subserve normal life, attempts to do so by the arousing of certain powers over which we normally have little or no control. This theory appears under different names, "Double Consciousness," "Das Doppel-Ich," etc., and the principle on which it depends is largely admitted by science. William James, for example, says: "In certain persons, at least, the total possible consciousness may be split into parts which co-exist, but mutually ignore each other."