But of this more fully hereafter.[Part II, Sect.

5.] There is another difference betwixt these two kinds of ideas, which is no less evident, namely that though neither the ideas, of the memory nor imagination, neither the lively nor faint ideas can make their appearance in the mind, unless their correspondent impressions have gone before to prepare the way for them, yet the imagination is not restrained to the same order and form with the original impressions; while the memory is in a manner tied down in that respect, without any power of variation.
It is evident, that the memory preserves the original form, in which its objects were presented, and that where-ever we depart from it in recollecting any thing, it proceeds from some defect or imperfection in that faculty.

An historian may, perhaps, for the more convenient Carrying on of his narration, relate an event before another, to which it was in fact posterior; but then he takes notice of this disorder, if he be exact; and by that means replaces the idea in its due position.

It is the same case in our recollection of those places and persons, with which we were formerly acquainted.

The chief exercise of the memory is not to preserve the simple ideas, but their order and position.