Here's a tidbit on Reformation epistemology from a critique of the new emerging church movement (good, though perhaps not as rounded as it should be, as Scot McKnight mentions)

"Scripture is the Word of God because it carries with it the authority of the author, God himself. This is not a rational construct, though it does not contradict reason. Instead the Reformers offered an approach that distinguished carefully between God as the principium essendi (essential foundation) of all theology and Scripture as the principium cognoscendi (cognitive foundation) of revealed theology. The authority of Scripture as the cognitive foundation is not found in a rational method for demonstrating reliability; but Scripture presupposes God, the essential foundation, while at the same time teaching us who God is."