Having the whole vast store of all present and past experiences to draw upon, he selects only those groups and those isolated instances that are related to our general interests and aims.  He disregards others.

[Sidenote:  How the Attention Works]

The attention operates in a manner complementary to the general Laws of 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.

Consciousness is a momentary thing. It is a passing state.  It is ephemeral and flitting.  It is made up in part of present sense-impressions and in part of past experiences.  These past experiences are brought forth from subconsciousness.  Some are voluntarily brought forth.  Some present themselves without our conscious volition, but by the operation of the laws of association and dissociation.  Some we seem unable voluntarily to recall, yet they may appear when least we are expecting them.  It is these last to which we have referred as lost in subconscious forgetfulness.  As a matter of fact, none are ever actually lost.

[Sidenote:  Making Experience Count]

All the wealth of your past experience is still yours—­a concrete part of your personality.  All that is required to make it available for your present use is a sufficient concentration of your attention, a concentration of attention that shall dwell persistently and exclusively upon those associations that bear upon the fact desired.

The tendency of the mind toward dissociation, a function limiting the indiscriminate recall of associated “groups,” is also manifested in all of us in the transfer to unconsciousness of many muscular activities.