We exhort you not to listen to those who say that today the issue of usury is present in name only, since gain is almost always obtained from money given to another. How false is this opinion and how far removed from the truth! We can easily understand this if we consider that the nature of one contract differs from the nature of another. – Vix Pervenit

Understanding usury requires an understanding of how the nature of some contracts differs, fundamentally and categorically, from the nature of others. Usury is not a matter of the same kind of contract differing only by ‘excessive interest’. Usurious contracts constitute a kind of contract which is intrinsically immoral by its very nature. This FAQ is intended to help people understand what usury is – and is not – and answer many of the questions which naturally arise.

[Note: this FAQ is also available in the form of a public domain ebook. It is also available as a hard copy book.]

Usury is lending money for profitable interest. The term “usury” often specifically refers to the interest itself – interest charged on a mutuum (personally guaranteed by the borrower) loan.

Lending is an agreement between a lender and a borrower, wherein the lender gives property to the borrower and the borrower pledges to “return it” later. The phrase “return it” might mean returning the actual property which was lent, or it might mean returning some different property – typically the same kind and in the same amount. It is the latter Kansas pawn shops sort of lending which is the context for usury: borrowing money or sugar, not borrowing a lawn mower or hedge trimmer.

In this kind of lending, the loan is a contract wherein the borrower is personally obligated, by his own agreement, to return the principal amount of the loan to the lender at some future time: not a specific object lent, but a specific amount lent. This is traditionally called a “mutuum”.

St. Thomas Aquinas defines a loan as a contract in which “the borrower holds the money at his own risk and is bound to pay it all back”: that is, the lender has recourse to the borrower himself to recover the loaned amount.

A full recourse/personally guaranteed/mutuum loan is a loan in which the lender’s claim against the borrower remains even if the borrower ‘consumes’ the proceeds

‘Consume’ is not meant in the sense that what is lent is literally destroyed (although it might be, if it is for example food); but merely that it can be alienated from the borrower without destroying the borrower’s obligation to the lender.

The lender’s claim in the contract is against the personal IOU of the borrower and is not confined to some specified property which either the borrower or lender possesses or which is purchased with the proceeds

The modern terms ‘loan’ and ‘debt’ can mean different things. When reading old books and documents on usury it is important to keep in mind that the word ‘loan’ in English translations is almost always a translation of ‘mutuum’ or the like. It refers specifically to loans secured by the personal guarantee of the borrower, sometimes called a ‘loan for consumption’. Not all modern ‘debt’ or ‘loans’ are secured by the personal guarantee of a borrower or borrowers.

Usury is always immoral no matter what interest rate is charged. The idea that usury is only charging “unreasonable” interest is a modern fiction. Usury is not an “unreasonable” rate of interest: it is any interest whatsoever as a term of agreement in a particular kind of contract, the mutuum loan.