[This post was originally written for Modern Paleo.]

Lately, I’ve begun re-reading Leonard Peikoff’s book Ominous Parallels. In the second chapter, I was struck by the clarity of his explanation of what philosophy studies. People are often baffled by the very subject of philosophy: they confuse it with religion, psychology, or anthropology. When teaching introductory philosophy courses in graduate school, I always spent a class or two on philosophy itself, so that my students wouldn’t be utterly confused about the purpose of the course.

So for anyone not quite clear, these paragraphs might be illuminating:

Philosophy is the study of the nature of existence, of knowledge, and of values.

The branch of philosophy that studies existence is metaphysics. Metaphysics identifies the nature of the universe as a whole. It tells men what kind of world they live in, and whether there is a supernatural dimension beyond it. It tells men whether they live in a world of solid entities, natural laws, absolute facts, or in a world of illusory fragments, unpredictable miracles, and ceaseless flux. It tells men whether the things they perceive by their senses and mind form a comprehensible reality, with which they can deal, or some kind of unreal appearance, which leaves them staring and helpless.

The branch of philosophy that studies knowledge is epistemology. Epistemology identifies the proper means of acquiring knowledge. It tells men which mental processes to employ as methods of cognition, and which to reject as invalid or deceptive. Above all, epistemology tells men whether reason is their faculty of gaining knowledge, and if so how it works–or whether there is a means of knowledge other than reason, such as faith, or the instinct of society, or the feelings of the dictator.

The branch of philosophy that studies values is ethics (or morality), which rests on both the above branches–on a view of the world in which man acts, and of man’s nature, including his means of knowledge. Ethics defines a code of values to guide human actions. It tells men the proper purpose of man’s life, and the means of achieving it; it provides the standard by which men are to judge good and evil, right and wrong, the desirable and the undesirable. Ethics tells a man, for instance, to pursue his own fulfillment–or to sacrifice himself for the sake of something else, such as God or his neighbor.

The branch of philosophy that applies ethics to social questions is politics, which studies the nature of social systems and the proper functions of government. Politics is not the start, but the product of a philosophic system. By their nature, political questions cannot be raised or judged except on the basis of some view of existence, of values, and of man’s proper means of knowledge.

Of course, the best overall introduction to philosophy is Ayn Rand’s essay “Philosophy: Who Needs It?” in her anthology Philosophy: Who Needs It. Nothing beats that.