The foregoing explanations show, firstly, why a post-hypnotic suggestion is carried out without the will, or in spite of it; and secondly, why this happens in spite of the apparent loss of memory. A second question is this: Why is a post-hypnotic suggestion carried out at the right moment ? We already know (p. 162) that the moment may be appointed in numerous ways; either by a concrete external signal - e.g., the striking of the clock, or by fixing an abstract period, or by counting signals or days.

In the case of the striking clock we shall find no new mental law; we find the same process quite commonly in normal life; it is the result of the association of ideas. The striking of the clock often reminds us of something we wanted to do at a particular time, and we then proceed to do it.

The same thing happens when we tie a knot in our handkerchief to remind ourselves of something. It occurs to me that I must write a letter to-morrow; I make a knot in my handkerchief to remind me of it. The knot and the letter are then associated in my consciousness, and when I see the knot next day the idea of writing the letter rises from my secondary into my primary consciousness. Now, we see the same thing in post-hypnotic suggestion (p. 162). The striking of the clock made the idea of taking the water-bottle and walking up and down with it rise from the secondary into the primary consciousness. This process of association is so powerful that it often takes effect even when the suggestion is not punctually carried out. I hypnotize X. on Saturday and tell him, "When you come in early on Tuesday I shall cough three times; you will then give me your hand and remark 'That is too stupid.'" X. does not come till Thursday, but the suggestion is carried out, merely because I cough.

We will take the second case, where an abstract period of time was given instead of a concrete sign. Here the idea lay in the secondary consciousness until it resulted in the corresponding action. This was carried out because work goes on in the secondary consciousness. But the calculations which take place in the secondary consciousness are not always quite exact; hence it often happens that the suggestion is not carried out punctually when an abstract period of time is given. For this also many analogies may be found in ordinary life. I say to X., " Remind me in an hour to write a letter." X. is busy, and thinks no more of the letter, but nevertheless reminds me of it after some time. But as he has not looked at the clock, he is not punctual: the case is quite analogous to post-hypnotic suggestions, where there is generally no perfect punctuality. Some people suppose that in the few cases of striking punctuality some unconscious calculation of time takes place, like the unconscious regularity of our pulse and breathing.

This would imply the existence of unconscious mental activity quite independent of the secondary consciousness; the unconscious regularity of the pulse is never directly perceived, whereas the processes that go on in the secondary consciousness occasionally rise into the primary. But there is no necessity to assume any unconscious activity in our case. We know, in the first place, that there are persons who can calculate time with some exactitude when they are awake, and, in the second, that others can do the same in sleep - i.e., they can wake themselves at a definite time without hearing the clock strike. For further information on this point I refer the reader to pp. 162 and 163. In any case, the secondary consciousness of a person who carries out a post-hypnotic suggestion after a definite lapse of time has no greater task to perform than might be expected of it, considering what we already know concerning the primary and the secondary consciousness. Here, again, the most important point is that we need not assume any special faculty on the part of the hypnotic subject.

The third way of fixing time is by counting signals or units of time (minutes, hours, days, etc., cf. p. 164 et seq.). Gurney's explanation of this is grounded on the division of the consciousness into primary and secondary. While the primary consciousness is busy talking to the experimenter, the secondary works on independently, marking the signals - e.g., the shuffling of the feet, etc. When the tenth signal is given the suggestion is carried out, just as other suggestions are carried out at an appointed signal.

Gurney endeavours to explain many long-deferred suggestions just in the same way. As we have seen, in these also the execution of the suggestion may be ordered at the end of a series of minutes or hours or days, etc., instead of a definite date (p. 163). This may be explained in two ways. Perhaps the subject calculates the date after he has been given the number of days or weeks. Against this there is the fact that the subjects, when hypnotized in the intervening time, cannot give the date. We have the same sort of thing in Bramweirs experiments which I described on p. 163. In those of Gurney's cases in which the subjects were hypnotized in the intervening time they could count the days which had elapsed, or were to elapse, before the suggestion should be carried out, though they did not know the exact date. On this account Gurney supposes an action of the secondary consciousness in such cases. He thinks that the hypnotic subject's subconsciousness calculates days just as the waking person's primary consciousness does, and that is why the suggestion is carried out.

By accepting these different spheres of consciousness and also an independent activity of the secondary consciousness, we are better able to understand those hypnotic suggestions which are carried out in a state of complete loss of memory, for the suggested command remains fixed in the consciousness, even if it only be in that consciousness which we have described as the secondary. The punctual execution of such a suggestion is only comprehensible if we admit that the two states of consciousness are similarly equipped; and the explanations we have already given show that this is no mere hypothesis.