Lex naturalis, natural law, is a cornerstone of Aquinas’s system and his most consequential contribution to Western thought. Natural law, he says, is apparent in the regular workings of nature, including the movements of the planets and in the growth and formation of living things; in the self-evident truths of mathematics and geometry; and in the logical workings of the human mind. However, it takes reason to see them and recognize them as laws.
