  Natural law theory of law has its most distinctive characteristic in its account of purely positive law which, though “entirely” dependent for its legal status on the fact that it has been authoritatively posited by some persons(s) or institution, nonetheless shares in law’s characteristic of entailing—albeit presumptively and defeasibly—a moral obligation of compliance. About these rules of a positive legal system, Aquinas says that, though they certainly should be, and be presumed to have been, “derived from natural law”, they have their legal force only from their part in this posited system (ex sola lege humana vigorem habent: ST I-II, q. 95 a. 3).