In point of fact, most ideas belong to very many different situations, so that the interweaving of the associative tendencies may be highly complicated. These paragraphs will strike you as both difficult and clumsy; but, if you review the course of the whole chapter, you will perhaps agree that our attempt at formulation has been worth while. We began with Aristotle’s four rules, and found that they are logical and practical, and also that they may logically be reduced to one, the ‘law of association by contiguity.’ That law did not satisfy us; we agreed with James that the _brain_ associates and that _meanings_ are associated. So we went to the brain; and by the aid of meaningless syllables we traced the history of the associative tendencies. Coming back to psychology proper, we distinguished the fusion and the conjunction of mental processes, and noted that the experimental method does not yet permit us to follow the patterns of mental connection in the large; though the experiments already made furnish additional proof that the old ‘laws’ of association are psychologically valueless. Now, to conclude, we have sought, first, to bring all that we know of the associative tendencies under a single formula; and then, building upon that formula and upon our partial knowledge of the patterns of mental connection, to write a psychological law that shall replace the logical law of contiguity. We have had to safeguard and qualify, and to leave loose ends for individual variation; but at any rate we have something positive whereby to support our criticism of the doctrine of association. § 37. =Practice, Habit, Fatigue.=—The establishment of an associative tendency may be looked upon as the establishment of a _habit_ of brain-function; the learning of series of syllables improves with _practice_; and continued learning gives rise to _fatigue_. It is natural, therefore, that we should here pause to say something about these three things in their relation to psychology.