[Footnote: 3 _Studien_, vol. i. p. 2 and _passim_. At vol. ii. p. 31 it is stated that the teaching on just price is a corollary of the usury teaching. But Aquinas treats of usury in the article _following_ his treatment of just price.] Our view is that the teaching on usury was simply one of the applications of the doctrine that all voluntary exchanges of property must be regulated by the precepts of commutative justice. In one sense it might be said to be a corollary of the doctrine of just price. This is apparently the suggestion of Dr. Cleary in his excellent book on usury: 'It seems to me that the so-called loan of money is really a sale, and that a loan of meal, wine, oil, gunpowder, and similar commodities--that is to say, commodities which are consumed in use--is also a sale. If this is so, as I believe it is, then loans of all these consumptible goods should be regulated by the principles which regulate sale contracts. A just price only may be taken, and the return must be truly equivalent.'[1] This statement of Dr. Cleary's seems well warranted, and finds support in the analogy which was drawn between the legitimacy of interest--in the technical sense--and the legitimacy of a vendor's increasing the price of an article by reason of some special inconvenience which he would suffer by parting with it. Both these titles were justified on the same ground, namely, that they were in the nature of compensations, and arose independently of the main contract of loan or sale as the case might be. 'Le vendeur est en présence de l'acheteur. L'objet a pour lui une valeur particulière: c'est un souvenir, par exemple. A-t-il le droit de majorer le prix de vente? de dépasser le juste prix convenu? ... Avec l'unanimité des docteurs on peut trouver légitime la majoration du prix. L'évaluation commune distingue un double élément dans l'objet: sa valeur ordinaire à laquelle répond le juste prix, et cette valeur extraordinaire qui appartient au vendeur, dont il se prive et qui mérite une compensation: il le fait pour ainsi dire l'objet d'un second contrat qui se superpose au premier. Cela est si vrai que le supplément de prix n'est pas dû au même titre que le juste prix.'[2] The importance of this analogy will appear when we come to treat just price and usury in detail; it is simply referred to here in support of the proposition that, far from being a special doctrine _sui generis_, the usury doctrine of the Church was simply an application to the sale of consumptible things of the universal rules which applied to all sales. In other words, the doctrines of the just price and of usury were founded on the same fundamental precept of justice in exchange. If we indicate what this precept was, we can claim to have indicated what was the true centre of the canonist doctrine. [Footnote 1: _The Church and Usury_, p. 186.] [Footnote 1: Desbuquois, 'La Justice dans l'Echange,' _Semaine Sociale de France_, 1911, p. 174.]