That branch of philosophical inquiry regarding values, usually divided into the two categories of aesthetics and ethics.

The study of values and their types. These can be of four types, systemic, extrinsic, intrinsic and holarchic. Complex systems are of the latter two types.

One of the three branches of philosophy that deals with the study of values and ethical judgments, their truth and their justification.

Axiology, from the Greek axia (αξια, value, worth), is the study of value or quality. It is often thought to include ethics and aesthetics—philosophical fields that depend crucially on notions of value—and sometimes it is held to lay the groundwork for these fields, and thus to be similar to value theory and meta-ethics. The term was used in the 19th and early 20th centuries, but in recent decades, value theory has tended to replace it in discussions of the nature of value or goodness in general.