[Sidenote: _Two Classes of "Complexes"_]

Obviously, if absolutely all mental experiences are preserved, they
consist altogether of two broad classes of complexes: first, those that
are momentarily _active in consciousness_, forming part of the present
mental picture, and, second, all the others--that is to say, all past
experiences that are _not at the present moment before the mind's eye_.

There are, then, _conscious_ complexes and _subconscious_ complexes,
complexes of _consciousness_ and complexes of _subconsciousness_.

[Sidenote: _The Subconscious Storehouse_]

And of the complexes of subconsciousness, some are far more readily
recalled than others. Some are forever popping into one's thoughts,
while others can be brought to the light of consciousness only by some
unusual and deep-probing stimulus. And _the human mind is a vast
storehouse of complexes, far the greater part buried in
subconsciousness_, yet somehow, like impressions on the wax cylinder of
a phonograph, preserved with life-like truth and clearness.

Turn back for a moment to our definition of memory. You will observe
that its second essential element is Recall.

Recall is the process by which the experiences of the past are summoned
from the reservoir of the subconscious into the light of present
consciousness. We necessarily touched upon this process in a previous
book, in considering the Laws of Association, but here, in relation to
memory, we shall go into the matter somewhat more analytically.