§ 6. Obstructions in the Flow of Ideal Activity. — Ideal activity, like perceptual activity, may be successful or unsuccessful. In so far as it is unsuccessful, it tends, like perceptual activity, to persist with variation of procedure. The tendency is of course proportioned to the strength of the interest involved.

* The examples of constructiveness given in this section are elementary; but such complex constructions as the invention of the steamengine or novelwriting depend essentially on the same conditions.

The conditions which obstruct and delay the flow of ideas are of various kinds. The hitch may occur either on the reproductive or on the constructive side of the process. When it occurs on the reproductive side, it is merely what is called a failure to remember; as when we find ourselves unable to recall the name of a person or the title of a book. If we are sufficiently interested, such failure is followed by a more or less prolonged effort to recollect. In this effort we vary our procedure, using all the means which present themselves. Supposing it is the name of a person we are endeavouring to recall. We try various clues in succession. We fix attention on objects and circumstances connected with the person. We perhaps inquire of a bystander, or look in a book; or go through a list of names on the chance that we may hit on the right one.

When the hitch occurs on the constructive side, the mental processes which are directed to overcome it may be extremely complex. The guessing of riddles furnishes a good example. We have ideally to reproduce something which shall satisfy all the conditions of the riddle. Certain relations are given, and we have to find another term which shall fit in with these in a harmonious whole. We make trial after trial, we think of this, and then we think of that; but each suggested solution in turn, though it may fulfil part, fails to fulfil all conditions of the problem. Finally we may or may not succeed in completing the ideal scheme, by making the right guess. We may take as another example a case in which the flow of ideas is controlled by the urgency of a practical need. Suppose a man shut up in prison and bent on devising a mode of escape. Let us assume that the main difficulty lies in the height which has to be descended before he can reach the ground. The notion of letting himself down from a height by means of a rope may be familiar to him by past experience: but in this case he has no rope. What he needs therefore is something which will take the place of a rope, — something which will fit into his ideal scheme as the rope would if he had it. He may proceed to think of various expedients, and he may at last light on the idea of using his sheets and blankets. The first time this suggestion occurs to him, it may not help him out of his difficulty; but it comes nearer to what he wants than anything else he has thought of, therefore his mind tends to dwell on it, and to give it a new shape which will suit his purpose. At last he hits on the idea of tearing up the sheets and twisting them into a rope. Of course we are supposing that our supposed prisoner has not already heard of this expedient. We may assume that he is the first man who invented it. In this, as in similar instances, association by similarity plays an important part. His own case calls up to the mind of the man analogous cases in which ropes have been used. He then proceeds to work out his own case on parallel lines, in so far as the circumstances will admit.