Usury is the practice of making immoral monetary loans intended to unfairly enrich the lender. But what, for Christians, counts as an immoral loan?
For much of church history, any interest was considered immoral. The 12th canon of the First Council of Carthage (345) and the 36th canon of the Council of Aix (789) declared it to be reprehensible even for anyone to make money by lending at interest. But that view eventually changed, and today even the Vatican participates in modern banking.
Some Catholics have used this example to argue for other changes, such as contraception. As Jay Richards notes,
This argument has achieved a place in the pantheon of conventional wisdom. But is it correct? Did the Church’s change of teaching on usury constitute a doctrinal change?
No. What changed was our understanding of the nature and function of money, neither of which has doctrinal status. Once the understanding of money changed, the sin of usury ceased to be identified in any simple way with charging interest on money. This is development, not substantial change.
Unfortunately, the issue is complex. And its complexity provides fertile ground to plant the seeds of doubt about the stability of doctrine. We need to lay this mistake to rest.