Lex naturae … nihil aliud est nisi lumen intellectis insitum nobis a Deo, per quod cognoscimus quid agendum et quid vitandum. Hoc lumen et hanc legem dedit Deus homini in creatione.
The law of nature … is nothing other than the light of the intellect planted in us by God, by which we know what should be done and what should be avoided. God gave us this light or law in creation.
Thomas Aquinas, On the Ten Commandments (c. 1273).