Recall. It is an active principle not of association, but of
_dissociation_.

You choose, for example, a certain aim in life. You decide to become the
inventor of an aeroplane of automatic stability. This choice henceforth
determines two things. First, it determines just which of the sensory
experiences of any given moment are most likely to be selected for your
conscious perception. Secondly, it determines just which of your past
experiences will be most likely to be recalled.

Such a choice, in other words, determines to some extent the sort of
elements that will most probably be selected to make up at any moment
the contents of your consciousness.

[Sidenote: _Iron Filings and Mental Magnets_]

From the instant that you make such a choice you are on the alert for
facts relevant to the subject of your ambition. Upon them you
concentrate your attention. They are presented to your consciousness
with greater precision and clearness than other facts. All facts that
pertain to the art of flying henceforth cluster and cling to your
conscious memory like iron filings to a magnet. All that are impertinent
to this main pursuit are dissociated from these intensely active
complexes, and in time fade into subconscious forgetfulness.

[Sidenote: _The Compartment of Subconscious Forgetfulness_]

By subconscious forgetfulness we mean a _compartment_, as it were, of
that reservoir in which all past experiences are stored.