What is Aquinas’ argument against usury (lending money at interest)?

Aquinas’ argues that usury is itself unjust. He does this by attempting to prove that money does not exist in the same form as other possessions that can be lent. Aquinas compares food to money in the sense that its use consists of its consumption. It would not be lawful to sell wine for both the price of the object and the price of the objects consumption, as the very use of buying wine is to drink it (consume it). Alternatively possessions exist who’s usage does not lie in consumption such as houses or ships and can be lent or charged for borrowing. Aquinas suggests that because money has been created for transactions and must be consumed or lost upon use, charging interest on loans aligns with the unlawful selling of twice as expensive wine over the lawful charging of house borrowing. 

Aquinas then goes on to deconstruct his 7 found objections to usury not being a sin by rationalizing how taking interest could be unlawful in each objection. Principally, Aquinas’ arguments against the objections speak on God describing usury as lawful only for the sake of benefiting others (providing spiritual goods, desist people of falling to greed), and humans having moral errors within the act of usury and the governing of its lawfulness. Aquinas’ argument of the distinction of consumption within possessions serves as a self-explanatory idea that counters the objection of a silver vessel and a silver coin holding the same worth when it comes to usury. His argument would state if a belongings use lies in its consumption, taking interest on its borrowing cannot be lawful.