But it must be noted that something may be derived from the natural law in two ways:  first, as a conclusion from premises, secondly, by way of determination of certain generalities.  The first way is like to that by which, in sciences, demonstrated conclusions are drawn from the principles:  while the second mode is likened to that whereby, in the arts, general forms are particularized as to details:  thus the craftsman needs to determine the general form of a house to some particular shape.  Some things are therefore derived from the general principles of the natural law, by way of conclusions; e.g. that “one must not kill” may be derived as a conclusion from the principle that “one should do harm to no man”:  while some are derived therefrom by way of determination; e.g. the law of nature has it that the evil-doer should be punished; but that he be punished in this or that way, is a determination of the law of nature.

Accordingly both modes of derivation are found in the human law.  But those things which are derived in the first way, are contained in human law not as emanating therefrom exclusively, but have some force from the natural law also.  But those things which are derived in the second way, have no other force than that of human law.

Reply Obj. 1:  The Philosopher is speaking of those enactments which are by way of determination or specification of the precepts of the natural law.

Reply Obj. 2:  This argument avails for those things that are derived from the natural law, by way of conclusions.

Reply Obj. 3:  The general principles of the natural law cannot be applied to all men in the same way on account of the great variety of human affairs:  and hence arises the diversity of positive laws among various people.

Reply Obj. 4:  These words of the Jurist are to be understood as referring to decisions of rulers in determining particular points of the natural law:  on which determinations the judgment of expert and prudent men is based as on its principles; in so far, to wit, as they see at once what is the best thing to decide.

Hence the Philosopher says (Ethic. vi, 11) that in such matters, “we ought to pay as much attention to the undemonstrated sayings and opinions of persons who surpass us in experience, age and prudence, as to their demonstrations.” ________________________

THIRD ARTICLE [I-II, Q. 95, Art. 3]

Whether Isidore’s Description of the Quality of Positive Law Is
Appropriate?

Objection 1:  It would seem that Isidore’s description of the quality of positive law is not appropriate, when he says (Etym. v, 21):  “Law shall be virtuous, just, possible to nature, according to the custom of the country, suitable to place and time, necessary, useful; clearly expressed, lest by its obscurity it lead to misunderstanding; framed for no private benefit, but for the common good.”  Because he had previously expressed the quality of law in three conditions, saying that “law is anything founded on reason, provided that it foster religion, be helpful to discipline, and further the common weal.”  Therefore it was needless to add any further conditions to these.