Just price

The just price is a theory of ethics in economics that attempts to set standards of fairness in transactions. With intellectual roots in ancient Greek philosophy, it was advanced by Thomas Aquinas based on an argument against usury, which in his time referred to the making of any rate of interest on loans. It gave rise to the contractual principle of laesio enormis.

St Thomas Aquinas taught that raising prices in response to high demand was a type of theft.