To accept an interpretation of life upon authority is permissible only if we have looked into the foundations of the authority we accept. But if we must determine the foundations of the authority, we no longer accept authority on authority. Authority could be authority to us only if we already knew that it had the right to claim authority. Such could be the case only if we knew in advance the nature of that authority. Thus we would have a theory of being already taken for granted at the outset of our investigation.
Greg Bahnsen, Van Til’s Apologetic, Pg. 95-96