GREGORY IX 1227-1241
[From a letter to brother R. in fragments of Decree n. 69, of uncertain date]
448 He who loans a sum of money to one sailing or going to market, since he has assumed upon himself a risk, is [not] to be considered a usurer who will receive something beyond his lot. He also who gives ten solidi, so that at another time just as many measures of grain, wine, and oil may be payed back to him, and although these are worth more at the present time, it is probably doubtful whether at the time of payment they will be worth more or less, for this reason should not be considered a usurer. By reason of this doubt he also is excused, who sells clothing, grain, wine, oil, or other wares so that at a set time he receives for them more than they are worth at that time, if, however, he had not intended so to sell them at the time of the contract.