The just price is an economic theory rooted in ethics that seeks to establish standards of fairness for commercial transactions. With intellectual origins tracing back to ancient Greek philosophy, the concept aims to ensure that exchanges are equitable for all parties involved.
During the medieval period, St. Thomas Aquinas significantly advanced this theory, primarily as a moral argument against usury. In that historical context, usury was defined as charging any rate of interest on loans. This ethical framework eventually influenced legal and contractual principles, most notably the doctrine of laesio enormis, which addresses cases of extreme price imbalance in contracts.