Second Question: On the Distinction of Laws

St. Thomas, I-II, q. 91.

230. Law is divided first and immediately by reason of origin. And indeed by reason of origin together with subject, time, and extension: one law is eternal, supreme, independent, and altogether universal; another is temporal and particular, derived and participated from it in time. This latter, by reason of foundation or necessity together with promulgation, is divided into natural or necessary law, which necessarily arises from the very essences of things and is promulgated by reason, and positive or free law, which, added to natural law and placed beyond it, is placed by the free will of the legislator and needs special promulgation. These are also distinguished by reason of matter: for the things which are commanded or prohibited by natural law are from their nature and necessarily good or evil; the things which are commanded and prohibited by positive law alone are therefore only good or evil because commanded or prohibited. But positive law, by reason of the immediate author, is divine (which by reason of time and perfection is old or new) or human, which is ecclesiastical or canonical, or civil or political; and by reason of origin, promulgation, and expression it is written or preserved by use, that is, introduced by custom.

Between natural law and positive divine law there mediates hypothetical natural law, or natural-divine law, which, namely, participates in both (yet more in natural law than in positive law), because, given some hypothesis which depends upon the free will of God, obligation necessarily arises: thus, given revelation, there necessarily arises the obligation of believing; between natural and human positive law there mediates the law of nations, which in some way participates in the necessity of natural law, and yet has been introduced everywhere by universal custom.