Illusions of memory illustrate rather a process of wrong classing, that is to say, of wrongly identifying the present mental image with past fact, which is the initial step in all inference.

In this way they closely resemble those slight errors of perception which are due to erroneous classing of sense-impressions.

But since the intellectual process involved in assimilating mental elements is very similar to that implied in assimilating complex groups of such elements, we may say that even in these simple kinds of error there is something which resembles a wrong classing of relations, something, therefore, which approximates in character to a fallacy.
By help of this brief review of the nature and causes of illusion, we see that in general it may be spoken of as deviation of individual from common experience.

This applies to passive illusion in so far as it follows from the accidents of individual experience, and it still more obviously applies to active illusion as due to the vagaries of individual feeling and constructive imagination.

We might, perhaps, characterize all illusion as partial view, partial both in the sense of being incomplete, and in the other sense of being that to which the mind by its peculiar predispositions inclines.