erly vindicated, it is easy to see that, from the nature of its
subject-matter, it is intimately and, indeed, inseparably connected with
one branch of science. For it is obviously impossible to answer the
question, What can we know? unless, in the first place, there is a clear
understanding as to what is meant by knowledge; and, having settled this
point, the next step is to inquire how we come by that which we allow to
be knowledge; for, upon the reply, turns the answer to the further
question, whether, from the nature of the case, there are limits to the
knowable or not. While, finally, inasmuch as What can I know? not only
refers to knowledge of the past or of the present, but to the confident
expectation which we call knowledge of the future; it is necessary to
ask, further, what justification can be alleged for trusting to the
guidance of our expectations in practical conduct.

It surely needs no argumentation to show, that the first problem cannot
be approached without the examination of the contents of the mind; and
the determination of how much of these contents may be called knowledge.
Nor can the second problem be dealt with in any other fashion; for it is
only by the observation of the growth of knowledge that we can
rationally hope to discover how knowledge grows. But the solution of
the third problem simply involves the discussion of the data obtained
by the investigation of the foregoing two.

Thus, in order to answer three out of the four subordinate questions
into which What can I know? breaks up, we must have recourse to that
investigation of mental phenomena, the results of which are embodied in
the science of psychology.

Psychology is a part of the science of life or biology, which differs
from the other branches of that science, merely in so far as it deals
with the psychical, instead of the physical, phenomena of life.

As there is an anatomy of the body, so there is an anatomy of the mind;
the psychologist dissects mental phenomena into elementary states of
consciousness, as the anatomist resolves limbs into tissues, and tissues
into cells. The one traces the development of complex organs from simple
rudiments; the other follows the building up of complex conceptions out
of simpler constituents of thought. As the physiologist inquires into
the way in which the so-called "functions" of the body are performed, so
the psychologist studies the so-called "faculties" of the mind. Even a
cursory atten