In the case of a mortgage, the house was in theory not even purchased but pledged as security, but any income from it accrued to the lender. In the eleventh century, this became a favorite trick of monasteries. In 1148, it was made illegal: henceforth, all income was to be subtracted from the principal. Similarly, in 1187, merchants were forbidden to charge higher prices when selling on credit—the Church thereby going much further than any school of Islamic law ever had.
