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A posthypnotic suggestion refers to a suggestion which is given to a person when in a hypnotic state and which involves an action to be carried out later when the person is in their normal waking state. It can be given in heterohypnosis and self-hypnosis. Take the following example, which is simple and of no particular use in itself, except to demonstrate typical, posthypnotic behaviour. When in a hypnotic state, suppose you gave yourself a suggestion that when you awoke after five minutes you would have a tremendous desire to take off your right shoe, and that with each moment that passed this urge would become stronger and stronger until you took off your right shoe. If you were actually carrying this out you would use repetition and imagery. Now, in all probability, you would carry out this instruction. After five minutes had elapsed, you would find yourself thinking about your right shoe, your attention would more and more be directed at your right shoe. You will probably remember the posthypnotic suggestion, but still the urge to comply will get stronger and stronger and stronger, until you carried out what had been suggested.

If a posthypnotic suggestion is not carried out, two reasons are usually advanced to explain this. First, the person was not in a sufficiently deep enough trance. Second, the instruction was ridiculous, inconsiderate or improper. Let me take each of these in turn. The first explanation is certainly true in a number of occasions, but it is a fallacy to conclude the depth of hypnosis from the fact of whether or not a given posthypnotic suggestion is carried out. Posthypnotic suggestions, if reasonable, can be acted upon with the person being in a light, medium or very deep trance.

The second explanation has arisen largely from experimentation and stage shows. If you are given a ridiculous instruction, in either heterohypnosis or in self-hypnosis, then in all likelihood you will not comply. One may consider the above suggestion to take off your right shoe after five minutes, comes into such a category. If you do, then you may not carry out this particular posthypnotic suggestion. The same is true if the suggestion, in some way, went against your moral code. It appears that the super-ego, to use a Freudian concept, is always working and does not ‘go to sleep’. The point here is that these situations tend to arise in heterohypnosis, where a ridiculous suggestion is being used in experimental work to ‘demonstrate’ the existence of posthypnotic phenomenon; or by stage hypnotists who wish to create an amusing performance (at the cost of the volunteer). In self-hypnosis this is unlikely to arise because you are unlikely to give yourself ridiculous or improper posthypnotic suggestions.

The great importance of posthypnotic suggestions is their use in speeding up the induction process on future occasions and for deepening the trance state.

Characteristics of posthypnotic suggestions

We shall now use this posthypnotic suggestion to discuss some of their characteristics. First and foremost, posthypnotic suggestions do not occur only in heterohypnosis. There is no more difficulty in giving yourself a posthypnotic suggestion as being given one by another person. The only real difference, if there is one, is that human nature has a tendency to follow other people’s suggestions more readily than our own – especially if the other person is someone in authority. Second, the posthypnotic suggestion is to be carried out when you are in your normal waking state. It is an act to be carried out in the future when you are in a normal waking state. Whether you temporarily re-enter a state of hypnosis to carry out the act we shall discuss later.

The performance of a posthypnotic suggestion needs to be activated. It can be activated by a signal, such as snapping the fingers; a phrase, ‘when I say, “sleep” you will go into a deep trance state’; or some other signal, such as playing a particular piece of music (very popular with stage hypnotists). The signal should be simple and unambiguous. It does, however, require careful consideration. The signal should not be something that a person (the hypnotist on this occasion) does quite naturally. In other words, it should not be something that commonly occurs in everyday life. Snapping the fingers does not come into this category. Why? The hypnotist will always say, “When I snap my fingers, you will go into trance.” So the signal is very explicit to the hypnotist snapping his fingers. But even this can lead to a problem. Suppose a hypnotherapist gave this signal. Suppose that this particular hypnotherapist was being interviewed on TV and happened to illustrate giving posthypnotic suggestions by snapping his fingers (which he does so on the programme). You happened to be watching this programme because you heard your hypnotherapist was on TV. Lo and behold, you go into a trance! However, you would not remain in trance. Even so, it is not something you would have preferred to do on this occasion.

Commonly used signals by stage hypnotists become even more of a problem. Suppose a stage hypnotist suggested that when you heard the opening bars of Beethoven’s Fifth Symphony, you would “go to sleep”. You are driving home from the show, and listening to Classic FM, and they play Beethoven’s Fifth. You begin to close your eyes and lose control of the car. Not at all a happy experience. The problem here, as we shall point out later, is not cancelling the suggestion. It therefore acts as a posthypnotic suggestion. Why? Because the stage hypnotist says, “When you hear this” (and the music is then played), the suggestion is open-ended. It is not clear that it means only during this performance. The person being hypnotised may interpret the suggestion as meaning whenever he or she hears this particular piece of music. What we observe here is that suggestions given in trance can sometimes be interpreted as posthypnotic suggestions on the part of the person being hypnotised, even though the hypnotist did not mean it to be so. This is why common signals – whether actions, phrases or other signals – should be avoided at all costs.

When engaging in self-hypnosis, therefore, you must be careful. Avoid generalisations, like “When I snap my fingers I will bark like a dog”. This is something you would not like to do at a meeting when you happened to snap your fingers! What you want to say is, “When I next snap my fingers I will bark like a dog”. This is specific and not general and involves only the next act of snapping your fingers and not all future occasions. Of course, “barking like a dog” is a silly suggestion, but it illustrates the importance of being careful about giving posthypnotic suggestions even to yourself.

One way to avoid common phrases or actions is to combine a phrase and an action – where these would never occur together in common usage or by accident. In this case both the action and the phrase can be simple and of common usage, but would not occur together. Whatever signal you choose, the posthypnotic suggestion should make it absolutely clear that you will respond only when you yourself give it. Although this may have been assumed, it is much safer to incorporate it into the suggestions so that there is no doubt as to what you are expected to do. In other words, you will carry out the posthypnotic suggestion only when you yourself give the signal.

When giving a posthypnotic suggestion it is necessary to constantly repeat the signal. It should also include a safeguard so that it is not accidentally carried out in other circumstances in which it was not meant to. With some individuals a posthypnotic suggestion is long lasting while with others it wears off. Why is not clear. Repeating the posthypnotic suggestion at intervals, however,  will reinforce it.

Both in heterohypnosis and in self-hypnosis it is very useful to use a posthypnotic suggestion to speed up re-entering trance on future occasions. To observe its use in self-hypnosis see the following video clip of me using such a posthypnotic suggestion. [Video clip].

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Post Hypnotic Suggestions