An early account of the maxim is found in Prosper of Aquitaine's eighth book on the authority of the past bishops of the Apostolic See concerning the grace of God and free will, "Let us consider the sacraments of priestly prayers, which having been handed down by the apostles are celebrated uniformly throughout the whole world and in every Catholic Church so that the law of praying might establish the law of believing [ut legem credendi lex statuat supplicandi]".. "Credendi" and "supplicandi" are gerunds which are oblique cases of the infinitive, and so can be translated into English as "of praying/believing," or just "of prayer/belief," respectively. Whereas the more general maxim "Lex orandi, lex credendi" suggests a general relationship between the two, Prosper of Aquitaine's formulation establishes the credence of certain Christian doctrines by placing their source in the Church's authentic liturgical rites, thus describing the liturgy itself as a deposit of extra-Biblical Christian revelation (part of a body of extra-Biblical beliefs known more collectively as Apostolic tradition), to which, in addition to Scripture, those who wished to know true doctrine could also refer. This would later be contradicted by the "Sola Scriptura" principle of Martin Luther and the Reformation.
