and to investigate the nature of that behind the appearances, which they
call the reality. In their attempts to solve one or both of these
problems, thinkers are led to marvel how it is that we get to know
things at all; they are tempted to investigate the possibility of
knowledge, and are in this way side-tracked from the main problem.
Others in their investigations are struck with amazement at the
intricate organisation of the human mind; they leave the riddle of the
universe to study the processes of human thought, and examine as far as
they are able the phenomena of consciousness. Then thought itself claims
the attention of other philosophers; they seek to find what are the laws
of valid thought, what rules must be followed in order that through
reasoning we may arrive at correct conclusions. Others become attracted
to an investigation of the good in the universe, and their question
changes from "What is?" to "What ought to be?" Others interest
themselves in the problem of the beautiful, and endeavour to determine
the essence of the beautiful and of its appreciation. In this way the
subject of philosophy separates out into a number of branches. The study
of the beautiful is called Æsthetics; of the good, Ethics; of the laws
of thought, Logic; of the mind processes, Psychology; of the possibility
of knowledge, the Theory of knowledge; while the deeper problems of the
existence of things, of reality and unity in the universe, are generally
included under Metaphysics.

It need hardly be pointed out that all these branches are very closely
related, and that a discussion of any one of them involves to some
extent a reference to the others. One cannot, for example, attempt to
solve the great question of reality without touching upon the
possibility of knowledge, without some reference to the processes of the
human mind, and the standards of the validity of thought, of the good,
and of the beautiful.