Dwelling so long on the test for controlled association may have created the impression that this is a rather artificial and unusual type of mental performance; but in reality controlled association is a very representative mental process, and enters very largely into all forms of mental work. This is true in arithmetical work, for example. A pair of numbers, such as 8 and 3, has been linked in past experience with several responses; it means 83, it means 11, it means 5, and it means 24. But if you are adding, it means 11, and no other response occurs; if you are multiplying, it means 24, and only that response occurs. The mental set for multiplying facilitates the responses of the multiplication table and inhibits those of the addition table, while the mental set for adding does the reverse. Rapid adding or multiplying would be impossible without an efficient mental set. Thus in arithmetic, as in the tests, the mental set is an inner response to the task.

In reading, there is a mental set which is an inner response to the context, and which determines which of the several well-known meanings of a word shall actually be called to mind when the word is read. Presented alone, a word may call up any of its meanings, according to frequency, etc.; but in context it usually brings to mind just the one meaning that fits the context. The same is true of conversation.

The objective situation arouses a mental set that controls both thought and action. The situation of being in church, for example, determines the meanings that are got from the words heard, and controls the motor behavior to {385} fit the occasion. The subject, observing the situation, adjusts himself to it, perhaps without any conscious effort, and his adjustment facilitates appropriate mental and motor reactions, while inhibiting others.

A problem arouses a mental set directed towards solution of the problem. A difficult problem, however, differs from a context or familiar task or situation in this important respect, that the appropriate response has not been previously linked with the present stimulus, so that, in spite of ever so good a mental set, the right response cannot immediately be recalled. One must search for the right response. Still, the mental set is useful here, in directing the search, and keeping it from degenerating into an aimless running hither and thither. Problem solution is so different a process from smooth-running controlled association that it deserves separate treatment, which will be given it a few chapters further on, under the caption of reasoning.{386}