des docteurs on peut trouver legitime la majoration du prix.  L’evaluation commune distingue un double element dans l’objet:  sa valeur ordinaire a laquelle repond le juste prix, et cette valeur extraordinaire qui appartient au vendeur, dont il se prive et qui merite 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 supplement de prix n’est pas du au meme 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.]

The scholastic teaching on the subject of the rules of justice in exchange was founded on the famous fifth book of Aristotle’s Ethics, and is very clearly set forth by Aquinas.  In the article of the Summa, where the question is discussed, ’Whether the mean is to be observed in the same way in distributive as in commutative justice?’ we find a clear exposition:  ’In commutations something is delivered to an individual on account of something of his that has been received, as may be seen chiefly in selling and buying, where the notion of commutation is found primarily.  Hence it is necessary to equalise thing with thing, so that the one person should pay back to the other just so much as he has become richer out of that which belonged to the other.  The result of this will be equality according to the arithmetical mean, which is gauged according to equal excess in quantity.  Thus 5 is the mean between 6 and 4, since it exceeds the latter, and is exceeded by the former by 1.  Accordingly, if at the start both persons have 5, and one of them receives 1 out of the other’s belongings, the one that is the receiver will have 6, and the other will be left with 4:  and so there will be justice if both are brought back to the mean, I being taken from him that has 6 and given to him that has 4, for then both will have 5, which is the mean.’[1] In the following article the matter of each kind of justice is discussed.  We are told that:  ’Justice is about certain external operations, namely, distribution and commutation.  These consist in the use of certain externals, whether things, persons, or even works:  of things as when one man takes from or restores to another that which is his:  of persons as when a man does an