 Azpilcueta, moreover, maintained that the exchange of money is not unnatural, contradicting Aristotle and many Scholastics. He treated money like other merchandise, positing that the morality of exchanges which were not dependent on money as their object was equitable. There were different questions connected to exchange. One of these was whether, in the case of petty exchange, it was licit to take more than the legally fixed commission; this view was rejected, and the legal commission was seen as binding in conscience (Alonso-Lasheras 2011: 172–173). Another problem arose in relation to exchange bills because the value of money varied considerably between different places within the Spanish Empire, offering new possibilities of making and losing money. Spanish theologians such as Azpilcueta and Molina countered the suspicion of usury associated with this kind of business by means of an early version of purchasing power theory according to which the exchange rates between currencies are in equilibrium when their purchasing power, i.e., what can be bought with a certain amount of money, remains the same (Grice-Hutchinson 1952: 52–53; Alonso-Lasheras 2011: 179). Concerning the topic of lending money, authors like Molina justified taking interest, first, by the lucrum cessans, the amount of money that the lender could have made during the time it was on loan as a credit and, then, by the periculum sortis, the risk that he might lose his capital (Molina-DII II, 315).