ld be equally right. Or rather there could be
no question of right or wrong in the matter at all. I could not forbid any
thought to be there, could not compel it to make way for another, perhaps
exactly its opposite. Yet I do this continually. I never merely observe
what thoughts are in my own mind or in another's. For I have a constant
ideal, a plumb-line according to which I measure, or can measure, every
train of thought. And I can compel others to apply this same plumb-line to
their thoughts. This plumb-line is logic. It is the unique law of the mind
itself which concerns itself about no law of nature or of association
whatsoever. And however mighty a flood of conceptions and associations may
at times pour through me in consequence of various confused physiological
states of excitement affecting the brain, or in consequence of the
fantastic dance of the associations of ideas, the ego is always able in
free thought to intervene in its own psychical experiences, and to test
which combinations of ideas have been logically thought out and are
therefore right, and which are wrong. It often enough refrains from
exercising this control, leaving the lower courses of thought free play.
Hence the mistakes in our thinking, the errors in judgment, the thousand
inconsistencies and self-deceptions. But the mind can do otherwise, can
defend itself from interruptions and extraneous influences by making use
of its freedom and of its power to follow its own laws and no others. It
is thus possible for us to have not only psychical experiences but
knowledge; only in this way can truth be reached, and error rejected. Thus
science can follow a sure course. Thus alone, for instance, could the
great edifice of geometry and arithmetic have been built up in its
indestructible certainty. The progress from axiom to theorem and to all
that follows is due to free thought, obeying the laws of inference and
demonstration, and entirely unconcerned about the laws of association or
the natural laws of the nervous agitations, the electric currents, and
other plays of energy which may go on in the brain at the same time. What
have the laws of the syllogism to do with the temporary states of tension
in the brain, which, if they had free course, would probably follow lines
very different from those of Euclid, and if they chanced once in a way to
follow the right lines from among the millions of possibilities, would
certainly soon turn to different ones, and