Ethics, also known as moral philosophy, is a branch of philosophy that involves systematizing, defending, and recommending concepts of right and wrong behavior.

Major areas of study in ethics may be divided into 3 operational areas:

Each of these areas include many further sub-fields of study.

Meta-ethics is a field within ethics that seeks to understand the nature of normative ethics. The focus of meta-ethics is on how we understand, know about, and what we mean when we talk about what is right and what is wrong.

Meta-ethics came to the fore with G.E. Moore's Principia Ethica from 1903. In it he first wrote about what he called the naturalistic fallacy. Moore was seen to reject naturalism in ethics, in his Open Question Argument. This made thinkers look again at second order questions about ethics. Earlier, the Scottish philosopher David Hume had put forward a similar view on the difference between facts and values.

Studies of how we know in ethics divide into cognitivism and non-cognitivism; this is similar to the contrast between descriptivists and non-descriptivists. Non-cognitivism is the claim that when we judge something as right or wrong, this is neither true nor false. We may for example be only expressing our emotional feelings about these things. Cognitivism can then be seen as the claim that when we talk about right and wrong, we are talking about matters of fact.