Aquinas’s lex iniusta non est lex: a Test of Legal Validity
Abstract
Legal positivism understands natural law as performing classifying connections between morality and law as tests of legal validity: if a norm with some pretence to legality contradicts a moral good, it cannot be called a legal norm. The new natural law school, however, claims that natural law develops qualifying connections between morality and law: tests of legal validity are performed by non-moral criteria such as due enactment or efficacy, and morality determines not what the law is, but rather which law is legally binding and which is legally defective. This article will demonstrate that Aquinas’s endorsement of the lexeme lex iniusta non est lex cannot be interpreted in any of these senses. Rather, Aquinas’s strong version of natural law indicates clearly that it can indeed be a classifying criterion of positive law, and that it cannot be the only and exclusive criterion of legal validity.