So we may say that what the mind arrives at through this its one great way of acting, no matter which of these forms it takes on, except in the cases in which it is not true in its results to the realities, is Knowledge.
Thus we see that the terms and faculties of the older psychology can be arranged under this doctrine of Apperception without the necessity of thinking of the mind as doing more than the one thing.

It simply groups and combines its material in different ways and in ever higher degrees of complexity.
Apperception, then, is the one principle of mental activity on the side of its reception and treatment of the materials of experience.
There is another term very current in psychology by which this same process is sometimes indicated: the phrase Association of Ideas.

This designates the fact that when two things have been perceived or thought of together, they tend to come up together in the mind in the future; and when a thing has been perceived which resembles another, or is contrasted with it, they tend to recall each other in the same way.

It is plain, however, that this phrase is applied to the single thoughts, sensations, or other mental materials, in their relations or connections among themselves.

They are said to be "associated" with one another.