Reply Obj. 2: A principle of direction should be applicable to many; wherefore (Metaph. x, text. 4) the Philosopher says that all things belonging to one genus, are measured by one, which is the principle in that genus. For if there were as many rules or measures as there are things measured or ruled, they would cease to be of use, since their use consists in being applicable to many things. Hence law would be of no use, if it did not extend further than to one single act. Because the decrees of prudent men are made for the purpose of directing individual actions; whereas law is a general precept, as stated above (Q. 92, A. 2, Obj. 2).
Reply Obj. 3: "We must not seek the same degree of certainty in all things" (Ethic. i, 3). Consequently in contingent matters, such as natural and human things, it is enough for a thing to be certain, as being true in the greater number of instances, though at times and less frequently it fail. ________________________
SECOND ARTICLE [I-II, Q. 96, Art. 2]
Whether It Belongs to the Human Law to Repress All Vices?
Objection 1: It would seem that it belongs to human law to repress all vices. For Isidore says (Etym. v, 20) that "laws were made in order that, in fear thereof, man's audacity might be held in check." But it would not be held in check sufficiently, unless all evils were repressed by law. Therefore human laws should repress all evils.
Obj. 2: Further, the intention of the lawgiver is to make the citizens virtuous. But a man cannot be virtuous unless he forbear from all kinds of vice. Therefore it belongs to human law to repress all vices.
Obj. 3: Further, human law is derived from the natural law, as stated above (Q. 95, A. 2). But all vices are contrary to the law of nature. Therefore human law should repress all vices.
On the contrary, We read in De Lib. Arb. i, 5: "It seems to me that the law which is written for the governing of the people rightly permits these things, and that Divine providence punishes them." But Divine providence punishes nothing but vices. Therefore human law rightly allows some vices, by not repressing them.
I answer that, As stated above (Q. 90, AA. 1, 2), law is framed as a rule or measure of human acts. Now a measure should be homogeneous with that which it measures, as stated in Metaph. x, text. 3, 4, since different things are measured by different measures. Wherefore laws imposed on men should also be in keeping with their condition, for, as Isidore says (Etym. v, 21), law should be "possible both according to nature, and according to the customs of the country." Now possibility or faculty of action is due to an interior habit or disposition: since the same thing is not possible to one who has not a virtuous habit, as is possible to one who has. 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.
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.