St. Vincent of Lerins, in his 5th-century work, Commonitorium, set forth an important criteria for Christian doctrine called the "rule of faith,” which states that Christian faith and doctrine must be based on what has been believed "everywhere, always, and by all" (quod ubique, quod semper, quod ab omnibus).

This universal consensus on essential doctrines is a sign of their truth.

While aspects of the Faith can be expressed in new ways, they cannot be innovative. They must simply make the ancient faith clearer, more articulate and more understandable to the present age. Such expressions should conserve and consolidate the ancient faith, not alter or contradict it.

Furthermore, the Church has a role in authoritatively interpreting and teaching the faith that has been handed down. The rule of faith is found in the Church's living tradition. That which contradicts what has been believed everywhere, always and by all should be rejected.

St. Vincent's rule of faith thus champions both doctrinal stability and new, faithful expression of the truth. It seeks a middle road between rigid fundamentalism and unrestrained innovation.