We believe the Bible to be the infallible word of God because the Bible itself tells us that this is the case. The immediate objection is that this is a circular argument — which of course it is! But is it really different from saying we know that God is God because he says he is? Can circularity be avoided and, if so, how? There are those who suggest it can be avoided merely by refusing to make assumptions, and by allowing the evidence to speak for itself. But this is to make another set of assumptions about what constitutes evidence and how it does speak for itself. If we refuse to start with the assumption that the Bible tells the truth in claiming to be God’s word, we must start with another assumption: that it does not or may not tell the truth and, therefore, it is not or may not be God’s word. If we seek to avoid the obvious circularity of this latter approach by saying that we must test the Bible by certain objectively neutral facts, then who determines what is neutral and which facts are applicable? In the end, it becomes human reason that judges what is reasonable evidence about the nature of the Bible. As soon as we admit this, then we see that it is a choice of two opposing circular arguments: one that assumes the ultimate authority of God and his word, and the other that assumes the ultimate authority of unaided human reason. We must examine these two positions more closely in pursuing the basis of valid interpretation of the Bible. Perhaps it will emerge that one position is really an exercise in futility in that it undermines itself by its own assumptions.
Gospel-Centered Hermeneutics, 32-33.