Supported by this view of a universal determination of mental activity, there has arisen the idea of a special determination, likewise copied from natural science. The coming and going of our thoughts is ordinarily considered as an unregulated play, defying calculation. That order rules even here, that the train of thought is governed by similarity to the mental states just present, or by a previous connection with these mental states, was clearly recognized and expressed even in the times of Plato and Aristotle. Yet this had remained merely the knowledge of a curiosity; no theoretical use whatever was made of it. Now it was brought into connection with newly recognized physical facts. This determination of the trains of thought depends, according to Hobbes, on the fact that our ideas are connected with material movements within the nerves and other organs, and that these movements, when once started, cannot immediately cease, but must gradually be consumed by resistance. The laws of association are to him in the spiritual sphere, what the law of inertia is in the physical. To Hume, a hundred years later, they depend on a kind of attraction, an idea suggested by Newton’s law of gravitation. And since inertia and attraction had been recognized as the most important and fundamental causes of material processes, it was a natural thing to regard the laws of association, which had been compared with them, as the fundamental phenomena of mental life, and to derive from them as manifold and important consequences as had been done in the case of the physical world. So arose the English associational psychology. It attempted to explain the traditional faculties of the mind, such as memory, imagination, judgment, and also the results of their combined activity (for instance, the consciousness of self and of the outer world) as natural and, so to speak, mechanical effects of the laws of association governing the processes of mind. No doubt this attempt, appearing also in a somewhat different form in the sensationalism of France, represents, in spite of its one-sidedness, a very great advance over the psychology of the past.
Just as associationism corresponds to the explanatory natural science of Galileo and Newton, the empirical psychology of the German enlightenment corresponds to the descriptive science of Linnæus and Buffon. But aside from a few exceptions, such as Tetens, its work must be regarded as a failure. To be sure, its intention is also to explain mental phenomena, to comprehend them first by careful introspection, and then to find by analysis the simplest faculties from which they have sprung. But its actual accomplishment does not go beyond a mere description of the occurrences offering themselves to first observation. And the results reached teach impressively that description is an unfruitful task unless, as sometimes of late, it is made to include also explanation. The numerous different expressions of mind, already distinguished by popular psychology, are only arranged in certain groups beside and above each other, and the explanation consists in presenting each expression as the effect of a special faculty. Thus we obtain a great multitude of complicated mental performances, inwardly related to each other, which are made to stand on a footing of equality and perfect independence, for example, perception, judgment, reason, imagination, and also abstraction, wit, symbolism, and so on. Like mere little _homunculi_ in the large _homo_, they act now in harmony, now in opposition. The poetic faculty, for example, “is a coöperation of imagination with judgment.” In connection with reason, imagination produces foresight. “Wit often does harm to judgment, and leads it to false verdicts.... Judgment must therefore be constantly on its guard against wit.” The advancement in this case did not result from a development of these views, but from their overthrow. But the opposition raised was turned also against associationism.