[Footnote 3: II. ii. 78, 2, ad. 4. Biel distinguishes three kinds of exchange: of goods for goods, or barter; of goods for money, or sale; and of money for money; and adds, 'In his contractibus ... generaliter justitia in hoc consistit quod fiant sine fraude, et servetur aequalitas substantiae, qualitatis, quantitatis in commutatis (_Op. cit._, IV. xv. 1). Buridan says that usury is contrary to natural law 'ex conditione justitiae quae in aequalitate damni et lucri consistit; quoniam injustum est pro re semel commutata pluries pretium recipere' (In _Lib. Pol._, iv. 6).] The difficulty which moderns find in understanding this teaching, is that it is said to be based on the sterility of money. A moment's thought, however, will convince us that money is in fact sterile until labour has been applied to it. In this sense money differs in its essence from a cow or a tree. A cow will produce calves, or a tree will produce fruit without the application of any exertion by its owner; but, whatever profit is derived from money, is derived from the use to which it is put by the person who owns it. This is all that the scholastics meant by the sterility of money. They never thought of denying that money, when properly used, was capable of bringing its employer a profit; but they emphatically asserted that the profit was due to the labour, and not to the money. Antoninus of Florence clearly realised this: 'Money is not profitable of itself alone, nor can it multiply itself, but it may become profitable through its employment by merchants';[1] and Bernardine of Sienna says: 'Money has not simply the character of money, but it has beyond this a productive character, which we commonly call capital.'[2] 'What is money,' says Brants, 'if it is not a means of exchange, of which the employment and preservation will give a profit, if he who possesses it is prudent, active, and intelligent? If this money is well employed, it will become a capital, and one may derive a profit from it; but this profit arises from the activity of him who uses it, and consequently this profit belongs to him--it is the fruit, the remuneration of his labour.... Did they (the scholastics) say that it was impossible to draw a profit from a sum of money? No; they admitted fully that one might _de pecunia lucrari_; but this _lucrum_ does not come from the _pecunia_, but from the application of labour to the sum.'[3] [Footnote 1: Quoted in Brants, _op. cit._, p. 134.] [Footnote 2: _Ibid._] [Footnote 3: Brants, _op. cit._, pp. 133-5; Nider, _De Cont. Merc._ iii. 15.]