What an Unjust Law Is

In one line

An unjust law is one that is validly made and ought not to have been made, and the tests for identifying one are that it treats people unequally without reason, that it takes away what it may not take away, that it was made or applied without fairness, or that its own purpose could not be stated in public.

In the wording a student can write in an exam: an unjust law is a rule which satisfies the formal requirements for validity in its legal system but violates the standards by which the content of law is judged, principally equality, the protection of basic interests, procedural fairness and the possibility of public justification; whether such a rule remains law is disputed between natural law theory, which holds that a sufficiently unjust rule is no law at all, and legal positivism, which holds that it is law and ought not to be obeyed.

The prior question: can a law be unjust at all?

Before you can ask what an unjust law is, you must be able to say that a law can be unjust, and two traditions answer differently.

Natural law. There is a standard above enacted law by which enacted law is judged, and a rule that fails badly enough is not law at all. The tradition's slogan is lex iniusta non est lex, an unjust law is not a law. On this view the citizen faced with such a rule is not facing a law and so faces no question of obedience.

Legal positivism. The existence of a law is one thing, its merit or demerit another. A rule enacted by a competent authority in the prescribed manner is law however wicked it is, and it should be described as law and then condemned.

Why the positivist position is the more useful one here, and Hart's reason for it. If a monstrous rule is said not to be law, the citizen's problem disappears by definition and the question of what to do about it is never asked. Saying "this is law, and it is too iniquitous to obey" states the problem accurately and keeps it open. A student who makes this point has understood the whole topic, and the point matters practically: a court in India does not say that section 377 was never law; it says the section was law and is now void.

Notice that Indian constitutional practice is a third thing, and is closer to natural law in effect while remaining positivist in form. A statute inconsistent with the Fundamental Rights is void, but it is void because a higher enacted rule says so, not because of a standard outside all enacted law.