These are the conditions of this very
inexact science, and we shall only know less of it by pretending to
know more, or by assigning to it a form or style to which it has not yet
attained and is not really entitled.

Experience shows that any system, however baseless and ineffectual, in
our own or in any other age, may be accepted and continue to be studied,
if it seeks to satisfy some unanswered question or is based upon some
ancient tradition, especially if it takes the form and uses the language
of inductive philosophy. The fact therefore that such a science exists
and is popular, affords no evidence of its truth or value. Many who have
pursued it far into detail have never examined the foundations on which
it rests. The have been many imaginary subjects of knowledge of which
enthusiastic persons have made a lifelong study, without ever asking
themselves what is the evidence for them, what is the use of them, how
long they will last? They may pass away, like the authors of them, and
'leave not a wrack behind;' or they may survive in fragments. Nor is it
only in the Middle Ages, or in the literary desert of China or of India,
that such systems have arisen; in our own enlightened age, growing up
by the side of Physics, Ethics, and other really progressive sciences,
there is a weary waste of knowledge, falsely so-called. There are sham
sciences which no logic has ever put to the test, in which the desire
for knowledge invents the materials of it.

And therefore it is expedient once more to review the bases of
Psychology, lest we should be imposed upon by its pretensions. The
study of it may have done good service by awakening us to the sense of
inveterate errors familiarized by language, yet it may have fallen into
still greater ones; under the pretence of new investigations it may be
wasting the lives of those who are engaged in it. It may also be found
that the discussion of it will throw light upon some points in the
Theaetetus of Plato,--the oldest work on Psychology which has come down
to us. The imaginary science may be called, in the language of ancient
philosophy, 'a shadow of a part of Dialectic or Metaphysic' (Gorg.).

In this postscript or appendix we propose to treat, first, of the true
bases of Psychology; secondly, of the errors into which the students of
it are most likely to fall; thirdly, of the principal subjects which
are usually comprehended under it; fourthly, of the form which facts
relating to t