 On natural law and other kinds of law Thomas again follows not Aristotle but the tradition of civil and canon law going back to the Roman  Stoics.[50]  He distinguishes divine law (eternal and positive) from human law, and among human laws he distinguishes natural law from the law of nations and civil law (see  Summa, 1–2, q. 95, a. 4).  Law is concerned with direction to the common good, which belongs to the whole people  (Summa, 1–2, q. 90, a. 3).  All positive human law must be in accordance with natural law, though its prescriptions will depend upon choice and circumstances (for example, natural law prescribes that we must not kill, but human positive law makes additional rules to prevent killing, rules that may depend on arbitrary choice—e.g., there may be a rule requiring motorists to drive on the left and not the right, or vice versa (see  Summa, 1–2, q. 95, a. 2).  Natural law is in effect morality, and according to Thomas the human mind, reflecting on and analysing human experience, can see the truth of various fundamental moral principles, which are thus “self-evident”, not in need of proof, and too fundamental to be capable of proof  (Summa, 1–2, q. 91, a. 3,  and  q. 94, a. 2).[51] 