I answer that, As Augustine says (De Civ. Dei ii, 21), quoting Tully, "a nation is a body of men united together by consent to the law and by community of welfare." Consequently it is of the essence of a nation that the mutual relations of the citizens be ordered by just laws. Now the relations of one man with another are twofold: some are effected under the guidance of those in authority: others are effected by the will of private individuals. And since whatever is subject to the power of an individual can be disposed of according to his will, hence it is that the decision of matters between one man and another, and the punishment of evildoers, depend on the direction of those in authority, to whom men are subject. On the other hand, the power of private persons is exercised over the things they possess: and consequently their dealings with one another, as regards such things, depend on their own will, for instance in buying, selling, giving, and so forth. Now the Law provided sufficiently in respect of each of these relations between one man and another. For it established judges, as is clearly indicated in Dt. 16:18: "Thou shalt appoint judges and magistrates in all its [Vulg.: 'thy'] gates . . . that they may judge the people with just judgment." It is also directed the manner of pronouncing just judgments, according to Dt. 1:16,17: "Judge that which is just, whether he be one of your own country or a stranger: there shall be no difference of persons." It also removed an occasion of pronouncing unjust judgment, by forbidding judges to accept bribes (Ex. 23:8; Dt. 16:19). It prescribed the number of witnesses, viz. two or three: and it appointed certain punishments to certain crimes, as we shall state farther on (ad 10).
But with regard to possessions, it is a very good thing, says the Philosopher (Polit. ii, 2) that the things possessed should be distinct, and the use thereof should be partly common, and partly granted to others by the will of the possessors. These three points were provided for by the Law. Because, in the first place, the possessions themselves were divided among individuals: for it is written (Num. 33:53,54): "I have given you" the land "for a possession: and you shall divide it among you by lot." And since many states have been ruined through want of regulations in the matter of possessions, as the Philosopher observes (Polit. ii, 6); therefore the Law provided a threefold remedy against the regularity of possessions. The first was that they should be divided equally, wherefore it is written (Num. 33:54): "To the more you shall give a larger part, and to the fewer, a lesser." A second remedy was that possessions could not be alienated for ever, but after a certain lapse of time should return to their former owner, so as to avoid confusion of possessions (cf. ad 3). The third remedy aimed at the removal of this confusion, and provided that the dead should be succeeded by their next of kin: in the first place, the son; secondly, the daughter; thirdly, the brother; fourthly, the father's brother; fifthly, any other next of kin. Furthermore, in order to preserve the distinction of property, the Law enacted that heiresses should marry within their own tribe, as recorded in Num. 36:6.
Secondly, the Law commanded that, in some respects, the use of things should belong to all in common. Firstly, as regards the care of them; for it was prescribed (Dt. 22:1-4): "Thou shalt not pass by, if thou seest thy brother's ox or his sheep go astray; but thou shalt bring them back to thy brother," and in like manner as to other things. Secondly, as regards fruits. For all alike were allowed on entering a friend's vineyard to eat of the fruit, but not to take any away. And, specially, with respect to the poor, it was prescribed that the forgotten sheaves, and the bunches of grapes and fruit, should be left behind for them (Lev. 19:9; Dt. 24:19). Moreover, whatever grew in the seventh year was common property, as stated in Ex. 23:11 and Lev. 25:4.
Thirdly, the law recognized the transference of goods by the owner. There was a purely gratuitous transfer: thus it is written (Dt. 14:28,29): "The third day thou shalt separate another tithe . . . and the Levite . . . and the stranger, and the fatherless, and the widow . . . shall come and shall eat and be filled." And there was a transfer for a consideration, for instance, by selling and buying, by letting out and hiring, by loan and also by deposit, concerning all of which we find that the Law made ample provision. Consequently it is clear that the Old Law provided sufficiently concerning the mutual relations of one man with another.