Abstract
Thomas Aquinas is generally known as an opponent of usury, which means any interest on a loan (i.e. any payment over the principal capital). The doctrine created by Aquinas can be called anti-usury doctrine.
In medieval economic and legal reality, other legal institutes, instead of the mutuum, had been applied for using things (real estate, chattels) without the transfer of their ownership - rent (locatio conductio rei), borrowing (commodatum) and leniency (precarium). In addition, the effects of the anti-usury (and anti-debt) doctrines caused the rise of the institute of agency.
In symbiosis with the development of agency, there were (regulated) markets as a tool to combat crime and create legal certainty for which the institute of agency was important; and markets were important for the proper function of agency.