A man addresses us who is like a figure seen by twilight; or we travel through countries where every feature of the scenery is vague; the outlines of the hills are ill-marked, and the rivers have no defined banks.

They are, in short, generic ideas of many past impressions of men, hills, and rivers.

An anatomist who occupies himself intently with the examination of several specimens of some new kind of animal, in course of time acquires so vivid a conception of its form and structure, that the idea may take visible shape and become a sort of waking dream.

But the figure which thus presents itself is generic, not specific.

It is no copy of any one specimen, but, more or less, a mean of the series; and there seems no reason to doubt that the minds of children before they learn to speak, and of deaf mutes, are peopled with similarly generated generic ideas of sensible objects.
It has been seen that a memory is a complex idea made up of at least two constituents.