The exchange of goods throughout history has certainly shaped the evolution of human civilization. With the ancient epiphany of tools and agriculture, societies created business to aid the collective wealth and wellbeing of the people. This achievement was surely a magnificent one but it gives ample room for the inherent greed of humankind to flourish. Such greed can be found in charging interest on loans, which was called usury in medieval Europe. The notion of a middleman cunningly "taking a cut" from a transaction became widespread and unavoidable, even until this day. The possibility of this practice being ethical has been debated since the idea was conceived. Civil law permitted usury at the time, and as people were naturally eager to extract money from nowhere, a great discussion on the matter ensued. St. Thomas declared that it is impossible to ethically charge interest on money lent unless the profit was spent on philanthropic necessities. His opinion on the matter was encoded in Catholic dogma for all believers to follow.
In the Summa Theologica, St. Thomas considers various moral objections to his stance on usury and supplies a rebuttal to each. Most notably, the theologian offers an objection regarding the difference between silver in the form of a vessel and silver in the form of coins. Requesting a price for the use of the vessel for a period of time is permitted in God's law. So should not the request of a price for the use of the coins be permitted too? The vessel and the coins of silver are both manufactured material things. They should not be regarded differently in business and in religious doctrine.