things that have happened to us, because
something in the present reminds us of them. Exactly the same present
fact would not call up the same memory if our past experience had been
different. Thus our remembering is caused by--

(1) The present stimulus,

(2) The past occurrence.

It is therefore a mnemic phenomenon according to our definition. A
definition of "mnemic phenomena" which did not include memory would,
of course, be a bad one. The point of the definition is not that it
includes memory, but that it includes it as one of a class of phenomena
which embrace all that is characteristic in the subject matter of
psychology.

(f) EXPERIENCE.--The word "experience" is often used very vaguely.
James, as we saw, uses it to cover the whole primal stuff of the world,
but this usage seems objection able, since, in a purely physical world,
things would happen without there being any experience. It is only
mnemic phenomena that embody experience. We may say that an animal
"experiences" an occurrence when this occurrence modifies the animal's
subsequent behaviour, i.e. when it is the mnemic portion of the cause of
future occurrences in the animal's life. The burnt child that fears the
fire has "experienced" the fire, whereas a stick that has been thrown on
and taken off again has not "experienced" anything, since it offers
no more resistance than before to being thrown on. The essence of
"experience" is the modification of behaviour produced by what is
experienced. We might, in fact, define one chain of experience, or one
biography, as a series of occurrences linked by mnemic causation. I
think it is this characteristic, more than any other, that distinguishes
sciences dealing with living organisms from physics.

The best writer on mnemic phenomena known to me is Richard Semon, the
fundamental part of whose theory I shall endeavour to summarize before
going further:

When an organism, either animal or plant, is subjected to a stimulus,
producing in it some state of excitement, the removal of the stimulus
allows it to return to a condition of equilibrium. But the new state
of equilibrium is different from the old, as may be seen by the changed
capacity for reaction. The state of equilibrium before the stimulus may
be called the "primary indifference-state"; that after the cessation
of the stimulus, the "secondary indifference-state." We define the
"engraphic effect" of a stimulus as the effect in making a difference