Thomas Aquinas

“ Now human law is framed for a number of human beings, the majority of whom are not perfect in virtue. Wherefore human laws do not forbid all vices, from which the virtuous abstain, but only the more grievous vices, from which it is possible for the majority to abstain; and chiefly those that are to the hurt of others, without the prohibition of which human society could not be maintained: thus human law prohibits murder, theft and such like. ”

“ The purpose of human law is to lead men to virtue, not suddenly, but gradually. Wherefore it does not lay upon the multitude of imperfect men the burdens of those who are already virtuous, viz. that they should abstain from all evil. ”

“ Wherefore there is no virtue whose acts cannot be prescribed by the law. Nevertheless human law does not prescribe concerning all the acts of every virtue: but only in regard to those that are ordainable to the common good---either immediately, as when certain things are done directly for the common good---or mediately, as when a lawgiver prescribes certain things pertaining to good order, whereby the citizens are directed in the upholding of the common good of justice and peace. ”

“ For, since one man is a part of the community, each man in all that he is and has, belongs to the community; just as a part, in all that it is, belongs to the whole; wherefore nature inflicts a loss on the part, in order to save the whole: so that on this account, such laws as these, which impose proportionate burdens, are just and binding in conscience, and are legal laws. ”

“ Thus the same is not possible to a child as to a full-grown man: for which reason the law for children is not the same as for adults, since many things are permitted to children, which in an adult are punished by law or at any rate are open to blame. In like manner many things are permissible to men not perfect in virtue, which would be intolerable in a virtuous man. ”

“ I answer that, As stated above (A [4] ) , every law is directed to the common weal of men, and derives the force and nature of law accordingly. Hence the jurist says [*Pandect. Justin. lib. i, ff., tit. 3, De Leg. et Senat.] : "By no reason of law, or favor of equity, is it allowable for us to interpret harshly, and render burdensome, those useful measures which have been enacted for the welfare of man." Now it happens often that the observance of some point of law conduces to the common weal in the majority of instances, and yet, in some cases, is very hurtful. ”

“ Since then the lawgiver cannot have in view every single case, he shapes the law according to what happens most frequently, by directing his attention to the common good. Wherefore if a case arise wherein the observance of that law would be hurtful to the general welfare, it should not be observed. ”

“ Otherwise these imperfect ones, being unable to bear such precepts, would break out into yet greater evils: thus it is written (Ps. 30:33) : "He that violently bloweth his nose, bringeth out blood"; and (Mat. 9:17) that if "new wine," i.e. precepts of a perfect life, "is put into old bottles," i.e. into imperfect men, "the bottles break, and the wine runneth out," i.e. the precepts are despised, and those men, from contempt, break into evils worse still. ”