In the Hermeneutics course I am taking, a definition of "Regula Fidei" was posed that seemed different from the way my Catholic acquaintances use the term. How is the term Rule of Faith used differently by Catholics than by Protestants? Specifically how is the practical application different even if the concept is similar in definition?
The rule of faith (Latin: regula fidei) or analogy of faith (analogia fidei) is a phrase rooted in the Apostle Paul's admonition to the Christians in Rome in the Epistle to the Romans 12:6, which says, "We have different gifts, according to the grace given us. If a man's gift is prophesying, let him use it in proportion to his faith."
The rule of faith is the name given to the ultimate authority or standard in religious belief, such as the Bible alone, as among some Protestants; the Bible and tradition, as among Catholics; reason alone, as among rationalists; as among the Eastern Orthodox it is theoria the inner light of the spirit, as among mystics.
In the Roman Catholic Church, the Bible and Sacred Tradition (that is, things believed to have been taught by Jesus and the apostles that were not recorded in the Bible but were transmitted through the church) are considered a rule for all believers for judging faith and practice.
In conservative Protestantism Romans 12:6 is viewed as the biblical reference for the term "analogy of the faith" (i.e., αναλογἰα τῆς πἰστεως). The Bible alone is considered the word of God and the only infallible standard for judging faith and practice; hence, for conservative Protestantism, the analogy of the faith is equivalent to the analogy of scripture – that is, opinions are tested for their consistency with scripture, and scripture is interpreted by the Holy Spirit speaking in scripture (compare sola scriptura).
In Methodism, John Wesley described a quadrilateral of faith, which held that Scripture, Reason, Experience and Tradition were interdependent.
By and large, Protestants don't really use the Rule of Faith as it is classically known. So to answer your question would be rather difficult since Protestantism has chosen to separate itself (potentially too much) from classical Catholicism. And I only say this because I sincerely doubt many protestants even know what the Rule of Faith even is.