their ordinary work, or injuries to the optic nerve or to the visual
center in the brain, make it impossible for us to see.

These facts are so self-evident that it seems useless to state them. One
has but to hold his hands before his eyes to convince himself that the
mind sees by means of eyes, which are physical sense organs. One has but
to hold his hands tight over his ears to find out that he hears by
means of ears--again, physical sense organs.

But simple and self-evident as the facts are, their acceptance must have
tremendous consequences to our thinking, and to our view of human
nature. If the mind is dependent in every feature on the body with its
sense organs, this must give to this body and its sense organs an
importance in our thought and scheme of things that they did not have
before. This close dependence of mind upon body must give to the body a
place in our scheme of education that it would not have under any other
view of the mind. We wish to emphasize here that this statement of the
close relation of the mind and body is not a theory which one may accept
or not. It is a simple statement of fact. It is a presupposition of
psychology. By "presupposition" is meant a fundamental principle which
the psychologist always has in mind. It is axiomatic, and has the same
place in psychology that axioms have in mathematics. All explanations of
the working of the mind must be stated in terms of nerve and brain
action, and stimulation of sense organs.

Since the sense organs are the primary and fundamental organs through
which we get experience, and since the sensations are the elementary
experiences out of which all mental life is built, it is necessary for
us to have a clear idea of the sense organs, their structure and
functions, and of the nature of sensations.