In Summa Theologica, Aquinas addressed questions like, Is it lawful to sell a thing for more than it’s worth? What about making a profit? Or charging interest? His answers indicate that what the law says is just is not always virtuous:
It is lawful to sell a thing for more than it is worth. In the commutations of human life, civil laws determine that
which is just.
Gain which is the end of trading, though not implying, by its nature, anything virtuous or necessary, does not, in itself, connote anything sinful or contrary to virtue: wherefore nothing prevents gain from being directed to some necessary or even virtuous end, and thus trading becomes lawful.
Accordingly, if without employing deceit the seller disposes of his goods for more than their worth, or the buyer obtain them for less than their worth, the law looks upon this as licit, and provides no punishment for so doing, unless the excess be too great.
Money … is by its very nature unlawful to take payment for the use of money lent, which payment is known as usury: and just as a man is bound to restore other ill- gotten goods, so is he bound to restore the money which he has taken in usury.
Price is “a metaphor for ethical and religious behavior and the power of the state to intervene in everyday life,” Charles Geisst writes in Just Price and the Markets.
A just price is more complicated. A just price is “a notion that sale items had intrinsic worth that may have differed from the asking price,” he says. “A value to which both parties could agree without hurting either unduly.”
The idea began with Aristotle, who argued that a fair price benefits both parties involved in an exchange. But it was Thomas Aquinas who brought Aristotle to the medieval European world. In the medieval church, the notion of a just price took a fuller form. In Summa Theologica, Aquinas discusses theology and human affairs, and he considers all by both faith and reason. Matters of money, naturally, are included. But Aquinas’ interpretation uniquely incorporated the work of the Philosopher: “Like his intellectual mentor, Aristotle, the discussion was not sales from a practical or legal standpoint but as matters of ethics. Aquinas, like Aristotle, used sales and contracts as metaphors for challenges that human behavior could present to the path of righteousness.”
“No secular source would be more important than the introduction of Aristotle’s works and their adoption by Thomas Aquinas in the thirteenth century,” Geisst says.
For Aquinas, matters of economy always come down to virtue. And a just price propels a virtuous market for the common good.
The concept, which today takes the form of the law of one price, has taken a number of forms since the 13th century. Aquinas’ work is reflected in each of them, from the development of standard measures to protect against fraud to protection from price gouging, especially for the poor; John Locke’s emphasis on a price free from deception to Adam Smith’s market price. The principle informs the gold standard implemented in the 1870s. The concept became global economic law, and rightly so, Geisst explains: “Modern technology helped it transform into an economic ‘law’ recognized universally.”
In Summa Theologica, Aquinas addressed questions like, Is it lawful to sell a thing for more than it’s worth? What about making a profit? Or charging interest? His answers indicate that what the law says is just is not always virtuous.