Five branches of philosophy mysteriously omits axiology. Usually listed among the six branches, axiology is sometimes first mentioned, e.g.: "axiology, metaphysics, epistemology, ethics, aesthetics, logic." Some lists also include "political philosophy," which studies government and deals with questions about the scope and legitimacy of public agencies.

Axiology is the study of value, the term having been coined in the late 19th Century, when questions of moral, aesthetic and logical value came to be taken together with what had traditionally been thought of mainly as economic worth.

There is intrinsic value, goodness for its own sake (e.g, virtue, beauty, knowledge, friendship) and extrinsic value, which refers to something valuaable only as a means toward something else.