Over at Called to Communion, Tim Troutman recalls a tough question that Bryan Cross once posed to a Reformed Christian:
“If Rome really were the Church, and you, as a Reformer, were actually in schism, how would you know it?” The Reformers have no answer except, “I would know it because Rome would be faithful to the Scriptures and I would be unfaithful.” But as [Reformed theologian Keith] Mathison stated, any appeal to Scripture is an appeal to private interpretation of Scripture. Therefore, the answer is really, “I would know it because Rome would agree with me.”
I think it's a very good question -- and one that would be difficult for a Reformed person to answer without devolving into "I'm right because I'm right" argumentation. In a future post, I'll attempt to take up the mirror-image of this question, which might be posed to a Catholic.