We have now discussed the extrinsic titles—­poena conventionalis, damnum emergens, lucrum cessans, and periculum sortis.  There were other grounds also, which cannot be reduced to the classification of extrinsic titles, on which more than the amount of the loan might be justly returned to the lender.  In the first place, the lender might justly receive anything that the borrower chose to pay over and above the loan, voluntarily as a token of gratitude.  ’Repayment for a favour may be done in two ways,’ says Aquinas.  ’In one way, as a debt of justice; and to such a debt a man may be bound by a fixed contract; and its amount is measured according to the favour received.  Wherefore the borrower of money, or any such thing the use of which is its consumption, is not bound to repay more than he received in loan; and consequently it is against justice if he is obliged to pay back more.  In another way a man’s obligation to repayment for favour received is based on a debt of friendship, and the nature of this debt depends more on the feeling with which the favour was conferred than on the question of the favour itself.  This debt does not carry with it a civil obligation, involving a kind of necessity that would exclude the spontaneous nature of such a repayment.’[1]

[Footnote 1:  II. ii. 78, 2, ad. 2.]

It was also clearly understood that it was not wrongful to borrow at usury under certain conditions.  In such cases the lender might commit usury in receiving, but the borrower would not commit usury in paying an amount greater than the sum lent.  It was necessary, however, in order that borrowing at usury might be justified, that the borrower should be animated by some good motive, such as the relief of his own or another’s need.  The whole question was settled once and for all by Aquinas:  ’It is by no means lawful to induce a man to sin, yet it is lawful to make use of another’s sin for a good end, since even God uses all sin for some good, since He draws some good from every evil....  Accordingly it is by no means lawful to induce a man to lend under a condition of usury; yet it is lawful to borrow for usury from a man who is ready to do so, and is a usurer by profession, provided that the borrower have a good end in view, such as the relief of his own or another’s need....  He who borrows for usury does not consent to the usurer’s sin, but makes use of it.  Nor is it the usurer’s acceptance of usury that pleases him, but his lending, which is good.’[1]

[Footnote 1:  II. ii. 78, 4.]

We should mention here the montes pietatis, which occupied a prominent place among the credit-giving agencies of the later Middle Ages, although it is difficult to say whether their methods were examples of or exceptions to the doctrines forbidding usury.  These institutions were formed on the model of the montes profani, the system of public debt resorted to by many Italian States.  Starting in the middle