Summa Theologiae Moralis, vol. I: De Principiis

On the Quality of Human Law.

S. Th. I-II, q. 95, a. 2 and 3.

270. Principle I. Human law is a derivation of natural law.

It is proved : Law, since it is an ordinance of reason, must be conformed to the rule of reason : for it is not true law unless it be just ; just is the same as right according to the rule of reason ; therefore, inasmuch as law has of justice or of the rectitude of reason, so much does it have of the virtue of law. But the first rule of reason is natural law. Therefore human law, inasmuch as it has of the virtue of law, has it insofar as it is derived from natural law. — If however in anything it disagrees with it, it will no longer be law but a corruption of law (Greg. XVI, enc. Qui pluribus, 9 Nov. 1846 ; Pius IX, enc. Quanta Cura, 8 Dec. 1864).

271. Principle II. Human law is the complement of natural law.

It is proved : From natural law something can be derived 1) as a necessary conclusion from the principles, e.g. one is not to kill from this, that evil is to be done to no one, and this pertains not to human law alone but also from the law of nature has the force of obliging ; 2) as a fitting conclusion or particular determination of a common and indeterminate principle, either for directing men or for compelling them, and this immediately has force from human law alone. Thus e.g. that a contract is to be made in such a way that better provision be made for justice, is a determination of the directive principle : contracts are to be entered into according to justice ; and that thieves are to be punished by prison rather than another penalty, is a determination of the coercive principle : thieves are to be punished.

It is said : immediately, because all just human laws oblige mediately by the force of this natural principle, that inferiors ought to obey superiors.

272. Principle III. Human law must be proportioned both to the end, and to natural and divine law.

It is proved : For human law is a means to an end, and is a rule and measure regulated and measured by the superior natural and eternal law of God ; therefore it must be proportioned to these three. Hence :

1. inasmuch as it is proportioned to the law of God, it must be congruous ;

2. and consequently honest, not contradicting the eternal law ; to religion inasmuch as it is conformed to natural law, it must be fitting to discipline, i.e. a) as to object : just, i.e. establishing what is right according to reason ; b) as to the faculty of acting or the power of the subjects : possible and according to nature, because impossible things are not to be imposed on men, and according to the custom of the country, because in living in society a man follows the manner of others, not bearing their burden ; c) as to due circumstances : fitting to place and time ;

3. inasmuch as it is proportioned to the end, it must be expedient for salvation or for the utility of men, and therefore a) necessary for removing evil or useful for obtaining good ; b) manifest, i.e. clear so that it can be understood, lest it be harmful to men ; c) handed down for the benefit of the commonwealth, i.e. ordered to the common good.