Ethics, sometimes known as moral philosophy, is a branch of philosophy that involves systematizing, defending and recommending concepts of right and wrong conduct, often addressing disputes of moral diversity. The term comes from the Greek word ἠθικός ethikos from ἦθος ethos, which means "custom, habit". The superfield within philosophy known as axiology includes both ethics and aesthetics and is unified by each sub-branch's concern with value. Philosophical ethics investigates what is the best way for humans to live, and what kinds of actions are right or wrong in particular circumstances. Ethics may be divided into three major areas of study: Meta-ethics, about the theoretical meaning and reference of moral propositions and how their truth values may be determined Normative ethics, about the practical means of determining a moral course of action Applied ethics draws upon ethical theory in order to ask what a person is obligated to do in some very specific situation, or within some particular domain of action Related fields are moral psychology, descriptive ethics, and value theory.