Hirschlaff certainly denies the existence of hypermnesia in hypnosis in toto, and considers the results as more probably due to unintentional suggestion. Other investigations of hypermnesia in hypnotics certainly belong to the domain of psychopathology. I may here recall the experiments of Breuer and Freud, who tried to discover an etiological moment in the production of hysteria by using the increased power of memory exhibited by hypnotics (cf. page 335). I also refer to what I said (page 349) concerning modern researches in hysteria, to the advancement of which hypnotism has greatly contributed, especially from the psychological point of view. I may further mention the impulsive actions and imperative ideas which we are able to induce experimentally by means of post-hypnotic suggestion. The presumption that what here occurs as the result of posthypnotic external suggestion appears in other cases as a pathological phenomenon produced by auto-suggestion, is certainly justified. Bentivegni has called attention to this affinity between post-hypnotic suggestions and many imperative ideas.

When the signal for a post-hypnotic action to be performed is perceived, the subject experiences certain impulses in the same way that a morbid person feels impelled to commit murder or suicide at the sight of a knife or of water (Cullerre). Hofler has pointed out the importance of post-hypnotic suggestion to normal psychology as well. He showed how it certainly stimulated research into the aftereffects of conclusions. I must here further refer to the creation of feelings and moods by means of post-hypnotic suggestion. We are able to arouse feelings of like and dislike without the subject being even conscious of the ideas connected with those feelings. A man's whole frame of mind may be made either pleasant or unpleasant without his ever knowing what influenced him, since he does not recollect the command he received. This likewise throws light on those cases in every-day life in which people are unable to explain why they feel in a good or bad frame of mind, as the case may be. Hypnotism and the theory of suggestion have also exercised a great influence on our estimation of synopsia, colour-audition, etc.

At the present day some of these phenomena are very properly considered the result of suggestion; others may be referred to associations of a purely psychological character, but not on that account attributable to suggestion. Others may possibly have a different origin - one of a purely physiological nature. At all events, the possibility of such phenomena originating in auto-suggestions was first put in its true light by hypnotism. Hypnotism has also done much to promote the study of sleep, and especially of dreams. By means of post-hypnotic suggestion we are certainly able to induce any dream we will.

There is another direction in which hypnotism has acquired importance. This brings me to the theory of primary and secondary consciousness. That there are subconscious mental acts was known long before the advent of modern hypnotism. But what we owe to hypnotism is a new, almost ideal method of putting such acts to the test of experiment. In this connection hypnotism has proved most fruitful. Post-hypnotic suggestion shows us how delicate the workings of the secondary consciousness sometimes are, and that, too, without there being any question of the presence of those automatic processes that practice unconsciously produces. A hypnotic is told that when he wakes he is to do something or other. He wakes, does not remember what has happened, and yet at the expiration of the hour performs the act more or less 'punctually. We are able to observe that the process of counting goes on in the secondary consciousness of our subjects; on this point I refer the reader to the experiments described on page 164. How accurately time is sometimes calculated in the secondary consciousness - i;e., how the secondary consciousness executes a complicated task - is shown by Delboeuf and Bramwell's experiments (p. 163), in which thousands of minutes were counted and estimated.

To the superficial observer, or the man who has no experience of hypnotism, many of these reports must appear incredible; yet these are just the very experiments that have been made, and their details recounted, by experienced and critical experimenters - by such a man as Delbceuf, in particular. Even if such experiments only succeed in a few cases, hypnotism has nevertheless provided us with an excellent method of testing the secondary consciousness experimentally.

A few investigators went even farther, and thought they were able to prove by means of hypnosis that the composite nature of human personality is the result of consciousness consisting of two halves, each of which operates more or less independently of the other. As Clemens Sokal and S. Landmann pointed out, these experiments have formed the essential part of French psychology for a number of years. I mention Binet as first and foremost in this respect, then F. Myers and Gurney in England. In Germany, Max Dessoir, who dedicated his Doppel-Ich to the subject, once held similar opinions, but he has latterly modified his views on the plurality of human personality very essentially.

In the same way, hypnotism has shed light on a problem that is usually considered to belong to philosophy, but that yet presents an essentially psychological side; I refer to the question of free-will. Post-hypnotic suggestion has shown the relative worthlessness of the feeling of free-will as a proof of its existence.

Spinoza's saying, "The illusion of free-will is nothing but our ignorance of the motives which determine our choice," appears to find striking support in post-hypnotic suggestion. If we suggest to a subject in hypnosis to move a chair when he wakes, he very frequently does as he was told. When asked to find a motive for the act, the subject sometimes replies that he felt compelled to act so, or sometimes says he believes he acted so of his own accord, and gives some reason or other for his action - anything but post-hypnotic suggestion. This feeling of freedom of will when there is actually an irresistible impulse at work has frequently been used as an argument in support of determinism. We see here that a state has been induced by experiment, in which the subject has the feeling that he is acting freely, while in reality his will has already been directed in a particular manner. Ribot, Forel and others have called attention to the light that post-hypnotic suggestion has thrown on the problem of free-will. The following experiment that I have frequently made, and that can be repeated by any one on a suitable subject, illustrates the illusion of free-will very clearly. I suggest to a hypnotic subject, X., to lay an umbrella on the ground after he wakes.