A personally guaranteed note looks, superficially, like the same sort of contract; but it isn’t. It – specifically the personal guarantee – isn’t a property interest in a thing. It attempts to assert a property interest in no thing: nothing. The fact that you cannot foreclose and collect your property demonstrates Aquinas’ point: the thing in which the contract asserts an ownership interest or other claim is no thing at all: nothing.
The apples have been eaten, the wine has been drunk, and the borrower has to take action to acquire new, different apples or wine precisely because the thing to which the mutuum lender lays claim does not exist
A mutuum for interest looks superficially like a census contract against a farmer’s field, as described by John de Lugo and affirmed as morally licit by Pius V. The difference is that there is no field: instead of representing a de-facto buy-leaseback of a claim against a field or other actual property, the personally guaranteed note represents a buy-leaseback of nothing at all.
32) In question 16 you say that the value of future labor is not a real asset which can be used as collateral on a for-profit loan. But wasn’t it relatively common before the modern era for people to be sold into slavery to pay off a debt?
Yes. Both are true. It is possible that moral waffling on chattel slavery kept the door open for usury in many peoples’ minds. Other people might see prison jobs as a kind of ‘slave labor’ and propose that it is immoral to throw people into prison just to get work out of them, even if they are willing to agree to it. But that kind of speculation and casuistry aside, clearly a slave’s future labor cannot, as a matter of objective fact, be alienated from the slave himself.