rom 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).]

[Footnote 2: The argument in favour of what we have called the
'objective' theory of the just price is strengthened by the
consideration that goods do not satisfy mere subjective whims, but
supply real wants. For example, food supplies a real need of the human
being, as also does clothing; in the one case hunger is appeased,
and in the other cold is warded off, just as drugs used in medical
practice produce real objective effects on the person taking them.]

The theory that the just price was objective seems to be accepted by
the majority of the best modern students of the subject. Sir William
Ashley says: 'The fundamental difference between the mediaeval and
modern point of view is... that with us value is something entirely
subjective; i