The challenge to objective values › What objectivity means here

Mackie's target is stronger than consistency, impartiality, or agreement. A rule could be applied consistently by a community without possessing objective authority. A person could also judge impartially while denying that values exist independently of human purposes.

His concern is with objective prescriptivity: a demand for action that is supposed to belong to the value itself, rather than derive its authority from someone's desire or an accepted institution. The demand purports to apply whether the person happens to want to comply.

Consider an original illustration. A rule in a chess club might prohibit late arrival because the members have agreed on a schedule. We can establish what that rule requires by consulting the agreement. A claim that deliberately humiliating a person is wrong, regardless of anyone's agreement, asks for a different kind of authority. Mackie thinks ordinary moral thought commonly makes that stronger claim.

This is not a denial that facts about harm, agreements, or motives can be objective in an ordinary sense. Whether an agreement was made and whether someone was injured can be factual questions. Mackie denies the further objectively prescriptive value, not every descriptive fact involved in evaluating a situation.