The development of the understanding of equal consideration through the rules of just price from antiquity to the beginning of the 20th century

The origin and subsequent development of the principle of equal consideration in contract law are closely related to the rules on just price. This paper traces the evolution of the just price concept from antiquity, including the principles of Roman law, medieval interpretations, and its application in canon law, to the first codifications in the 19th and 20th centuries. We will demonstrate how the understanding of just price has changed, under what conditions it should be applied, whether it should be legislatively regulated and to what extent, and how this legal institution illustrates and safeguards the principle of equal consideration in contract law. Furthermore, we will consider the entanglement of this institution with the institution of laesio enormis, whose evolution has significantly influenced the formation of the just price concept as we know it today.