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 AEsthetics; 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.