Peter Kreeft (Roman Catholic):HT: Kevin DeYoung
Most Protestants reject all Catholic doctrines they cannot find explicitly in Scripture–for example, Mary’s Assumption into heaven–because they believe sola scriptura: that Scripture alone is the infallible authority. This is the fundamental reason behind all the differences between Protestant and Catholic theology. (Catholic Christianity, 20).
Gary Dorrien (Liberal Protestant):
The essential idea of liberal theology is that all claims to truth, in theology as in other disciplines, must be made on the basis of reason and experience, not by appeal to external authority. Christian scripture may be recognized as spiritually authoritative within Christian experience, but its word does not settle or establish truth claims about matters of fact. (The Making of American Liberal Theology: Idealism, Realism, and Modernity, 1900-1950, 1)
Michael Horton (Evangelical Protestant):
Ultimate authority always resides outside the self and even outside the church, as both are always hearers of the Word and receivers of its judgment and justification. The church is commissioned to deliver this Word (a ministerial office), not to possess or rule it (a magisterial office). Thus, the authority is always transcendent. Even when it comes near us, it is never our own word that we hear (Ro. 10:6-13, 17). (The Christian Faith, 194)