hugo grotius, the founder of a purely rationalistic system of natural law, argued that law arises from both a social impulse—as aristotle had indicated—and reason. immanuel kant believed a moral imperative requires laws "be chosen as though they should hold as universal laws of nature". jeremy bentham and his student austin, following david hume, believed that this conflated the "is" and what "ought to be" problem. bentham and austin argued for law's positivism; that real law is entirely separate from "morality". kant was also criticised by friedrich nietzsche, who rejected the principle of equality, and believed that law emanates from the will to power, and cannot be labelled as "moral" or "immoral".