And just as we distinguished between those hallucinations of sense which arise first of all through some peripherally caused subjective sensation, and those which want even this element of reality and depend altogether on the activity of imagination, so we may mark off two classes of mnemonic hallucination.

The false recollection may correspond to something past--and to this extent be a recollection--though not to any objective fact, but only to a subjective representation of such a fact, as, for example, a dream.

In this case the imitation of the mnemonic process may be very definite and complete.
Or the false recollection may be wholly a retrojection of a present mental image, and so by no stretch of language be deserving of the name recollection.
It is doubtful whether by any effort of will a person could bring himself to regard a figment of his present imagination as representative of a past reality.

Definite and complete hallucinations of this sort do not in normal circumstances arise.

It seems necessary for a complete illusion of memory that there should be something past and recovered at the moment, though this may not be a real personal experience.[127] On the other hand, it is possible, as we shall presently see, under certain circumstances, to create out of present materials, and in a vague and indefinite shape, pure phantoms of past experience, that is to say, quasi-mnemonic images to which there correspond no past occurrences whatever.
All recollection, as we have seen, takes place by means of a present mental image which returns with a certain degree of vividness, and is instantaneously identified with some past event.