One argument from Catholicism against Sola Scriptura is that it is invalid because Scripture is not self-defining. That it the cannon is not found in Scripture, but is handed to us by Church authority and Tradition. This is particularly frustrating argument for me since when unbiblical notions are spoken of as the truth and I say, "That's not in the Bible," my Catholic relatives fall back on that argument. "It is only by tradition that you know what IS in the Bible. How can you say that there is no absolute truth outside of Scripture?" Anyone who could help, I'd apreciate it.