The preceding explanations are chiefly intended to approximate as much as possible post-hypnotic suggestion to certain habitual occurrences. There is no question of a complete identification of them. Still, I think I have proved that those properties which we are prone to consider characteristic of post-hypnotic suggestion are also met with out of hypnosis. There is one thing more which I must certainly point out as I have not hitherto mentioned it, and it might pass for a characteristic of hypnosis. I refer to the fact that it is not the post-hypnotic command itself - i.e., not what was said to the subject, but the idea of carrying out the command, that later on rises to the primary consciousness. If I suggest to a subject in hypnosis to ask for an apple an hour after he wakes, he will do so; it is not my order, but idea of carrying it out, that rises into his primary consciousness. We must always carefully distinguish between these two points.

But there are many analogies for this, also, where there is no question of hypnosis. We are reminded, for instance, of those dominant ideas which often result in actions, and whose origin is for the most part "unconscious" (Bentivegni). The source of the idea cannot be discovered by questions or by any other means. But we need not refer to Lock's principle, Nil est in intellectu, quod non prius fuerit in sensu, to justify the assumption that a dominant idea is the result of some external event that has formerly influenced the mind of the person concerned. Lcewenfeld has very properly pointed out the determining influence which certain mental impressions possess. A sudden fright, for instance, may produce a lasting dominant idea. Freud mentions the case of Pascal, who from the time he nearly fell into the Seine was constantly pursued by the idea of falling into an abyss. But even events that do not directly affect the emotions - for example, quite ordinary occurrences in normal life - can by suggestion produce such ideas. It is quite a common occurrence for a patient to feel convinced that he is suffering from severe cardiac trouble, because he has overheard some casual remark about heart disease.

Friedmann mentions the case of a girl who heard a scream just as she was going out of the room and was told that a neighbour's child had fallen out of the window. If ever after that she wished to open the door, the recollection of what had happened overcame her; this placed her in a most painful position, as she was never able to go out of the room, even to answer the calls of nature. It may very well happen that the original cause - the determining factor - is forgotten, yet the dominant idea will arise directly the same prompting impression occurs. This is analogous to post-hypnotic suggestion, where, as we have seen, it is the suggested idea, and not the command, that rises to the primary consciousness. The same sort of thing occurs when imperative ideas lead to uncontrollable acts - e.g., murder, suicide, incendiarism, etc. We may here include a possible cause of hysteria described by Breuer and Freud. They attribute the appearance of hysterical symptoms to some injury to the sexual organs which the patient has received in early youth but does not remember when in a normal waking state.

As we shall see in the medical section, Breuer and Freud employ hypnosis to bring back a forgotten injury to the patient's recollection, in the hope of affecting a cure thereby.

But it is not only under pathological conditions that some externally induced idea influences our actions and feelings without our being able to remember how the idea was implanted in us. Let us suppose that a child two or three years old is often in the society of A. and B.; A. is kind and gentle, B. hard and unkind, so that the child gradually learns to like A. and dislike B. Let us further suppose that the child sees neither for a long time; nevertheless, when it does meet them accidentally it will still like A. and dislike B. The child, who is now several years older, will not know its own reasons; it will not remember the former conduct of A. and B.; no questions will bring this back to its memory, yet the effect of the old impressions remains. It is certain that this is a common occurrence in childhood. Shrewd observers think it likely that a man may owe his preference for some profession - painting, for example - to some childish impression, such as dabbling with colours; in this case also the early impression is forgotten by the adult.

So far from this occurrence being confined to childhood we frequently observe it in adults. We are often influenced by unimportant expressions we have heard, though later on we cannot trace the effect to its cause. Our conduct with regard to experiences and theories is often the effect of early unconscious impressions. It is by no means an uncommon occurrence that a remark which has apparently passed unheeded has really produced a profound effect

Finally, we find something similar in the association of heterogeneous ideas. Recent studies in sexual perversion have drawn attention to the fact that the concurrence of sexual desire and some chance experience - witnessing a flogging for example - may lead to lasting sexual perversion. It may happen that the original experience is forgotten, and yet the link between flogging and sexual excitement remains fast, so that witnessing the former invariably induces the latter. Even when the association is of the simplest kind, depending on the law of the association of experiences, there is no necessity whatever for the original experience to be remembered; the effect corresponding to it invariably occurs. When two mental processes have once occurred together, recurrence of the one calls up the other. Here also, without any recollection of the concrete case in which the original linking together took place being necessary, a corresponding and similar linking invariably takes place. In short, these cases are analogous to post-hypnotic suggestions, which, as we have seen, are carried out although the command has apparently been forgotten.