自然法
Furthermore, in his "Treatise on Law", Thomas distinguished four kinds of law: eternal, natural, human, and divine. "Eternal law" is the decree of God that governs all creation: "That Law which is the Supreme Reason cannot be understood to be otherwise than unchangeable and eternal." "Natural law" is the human "participation" in the "eternal law" and is discovered by reason. "Natural law" is based on "first principles":