Norms Are Rules Third Parties Enforce

Unlike other social animals, humans uniquely have norms: rules about what one is supposed to do where, if a third party witnesses a violation, they are themselves expected to do something about it — report it, spread word, or pressure the violator to stop. Many such norms (help each other, don't brag, don't be violent, decide by consensus, avoid coalitions) are common across human cultures and are often expressed in terms of motives.