the philosophy of law is commonly known as jurisprudence. normative jurisprudence asks "what should law be?", while analytic jurisprudence asks "what is law?" john austin's utilitarian answer was that law is "commands, backed by threat of sanctions, from a sovereign, to whom people have a habit of obedience". natural lawyers on the other side, such as jean-jacques rousseau, argue that law reflects essentially moral and unchangeable laws of nature. the concept of "natural law" emerged in ancient greek philosophy concurrently and in connection with the notion of justice, and re-entered the mainstream of western culture through the writings of thomas aquinas, notably his "treatise on law".