one definition is that law is a system of rules and guidelines which are enforced through social institutions to govern behaviour. in "the concept of law" hart argued law is a "system of rules"; austin said law was "the command of a sovereign, backed by the threat of a sanction"; dworkin describes law as an "interpretive concept" to achieve justice in his text titled "law's empire"; and raz argues law is an "authority" to mediate people's interests. holmes said "the prophecies of what the courts will do in fact, and nothing more pretentious, are what i mean by the law." in his "treatise on law" aquinas argues that law is a rational ordering of things which concern the common good that is promulgated by whoever is charged with the care of the community. this definition has both positivist and naturalist elements.