interminable process of calculations, nobody could say authoritatively what precisely the value was, and in practice the determination of value had perforce to be left to the ordinary human estimate of what it was, which of its very nature was bound to admit a certain margin of fluctuation.  Thus we can easily understand how, even with an objective standard of value, the just price might be admitted to vary within the limits of the maximum as it might be expected to be estimated by sellers and the minimum as it would appear just to buyers.  The sort of estimation of which St. Thomas speaks is therefore nothing else than a judgment, which, being human, is liable to be slightly in excess or defect of the objective value about which it is formed.’[1] As Father Kelleher puts it on a later page, ’There is a sense certainly in which, with a solitary exception in the case of wages, it may be said with perfect truth that the common estimation determines the just price.  That is, the common estimation is the proximate practical criterion.’[2]

[Footnote 1:  Irish Theological Quarterly, vol. x. p. 166.]

[Footnote 2:  P. 173.]

Father Kelleher uses in support of his contention a very ingenious argument drawn from the doctrine of usury.  As we said in the first chapter, and as we shall prove in detail in the next section, the prohibition of usury was simply one of the applications of the theory of equivalence in contracts—­in other words, it was the determination of the just price to be paid in an exchange of money for money.  If, asks Father Kelleher, the common estimation was the final test of just price, why was not moderate usury allowed?  That the general opinion of the community in the Middle Ages was undoubtedly in favour of allowing a reasonable percentage on loans is shown by the constant striving of the Church to prevent such a practice.  Nevertheless the Church did not for a moment relax its teaching on usury in spite of the almost universal judgment of the people.  Here, therefore, is a clear example of one contract in which the standard of value is clearly objective, and it is only reasonable to draw the conclusion that the same standard which applied in contracts of the exchange of money should apply in contracts of the sale of other articles.

Father Kelleher’s contention seems to be completely supported by the passage from Nider which we have cited above, to the effect that the common estimation ceases to be the final test of the just price when the contracting parties know or believe that the common estimation has erred.[1] This seems to us clearly to show that the common estimation was but the most generally received test of what the just price in fact was, but that it was in no sense a final or irrefutable criterion.[2]

[Footnote 1:  De Cont.  Merc., ii. xv.  Nider was regarded as a very weighty authority on the subject of contracts (Endemann, Studien, vol. ii. p. 8).]