Complete the account of the border between law and its neighbours.

The positivist claim that what law is and what it ought to be are distinct questions is the separability thesis. Radbruch held that statutory law must yield where its conflict with justice becomes intolerable. Fuller called his eight requirements the internal morality of law. Hart replied to Austin that being obliged by a gunman is not the same as being under an obligation.

The four blanks hold the whole argument: a thesis about what the concept of law includes, a formula for when validity gives way, a list of the conditions a system must roughly satisfy to be one, and the distinction between a probability of harm and an internal attitude to a rule.