After the fall of the Nazis, the connections between law (which calibrates obedience against rule-adherence) and morality (which calibrates obedience against a normative good) acquired a renewed importance: the Nazis claimed to be operating under a legal system that differed in content but not in kind.

Some legal theorists agreed: the systemic integrity of a legal code said nothing about its content -- the law was simply whatever was posited by lawgivers. They were known as "positivists" for this reason. Meanwhile, those who took the so-called "natural law" position insisted that morality was not separable from the law in this fashion.

It was into this climate that the debate between positivist H L A Hart and natural lawyer Lon Fuller emerged. More than a half-century later, Dr Rundle explains why their debate has never really gone away.