When you have contrived to persuade him that, for Catholics, the authority of the Church in matters of faith is not a self-evident axiom, but a truth arrived at by a process of argument, the Protestant controversialist has his retort ready. "You admit, then, after all," he says, "that a man has to use his own private judgment in order to arrive at religious truth? Why, then, what is the use of authority in religion at all? I had always supposed that there was a straight issue between us, you supporting authority and I private judgment; I had always supposed that you criticised me for my presumption in searching for God by the light of my imperfect human reason; it proves, now, that you are no less guilty of such presumption than myself! Surely your reproaches are inconsistent, and your distinctions unnecessary. If you use your private judgment to establish certain cardinal points of theology, the existence of God, the authority of Christ, and so on, why may not I use my private judgment to establish not only these, but all other points of theology--questions such as the doctrine of the Blessed Trinity, or the Real Presence in the Eucharist? You can hardly blame me for using the very privileges which you have just claimed so eagerly for yourself."
I could not have imagined, if I had not heard it with my own ears, the accent of surprise with which Protestants suddenly light upon this startling discovery, that the belief we Catholics have in authority is based upon an act of private judgment. How on earth could they ever suppose we taught otherwise? I say nothing here of the grace of faith, which is the hidden work of God in our souls. But how could the conscious process by which we arrive at any form of the truth begin without an act of private judgment? I may, indeed, overcome by a kind of emotional crisis, surrender myself unreflectively to an influence imaginatively experienced; but that is not Catholicism, it is Protestantism; it is "conversion" in its crudest form. If I employ my reason at all; if I employ my reason only so far as to say "The Church says this, and the Church is infallible, therefore this must be true," even so I am using private judgment; it is my own reason which draws its conclusions from the syllogism. Reject private judgment? Of course Catholics have never rejected private judgment; they only profess to delimit the spheres in which private judgment and authority have their respective parts to play.
Is it really so difficult to see that a revealed religion demands, from its very nature, a place for private judgment and a place for authority? A place for private judgment, in determining that the revelation itself comes from God, in discovering the Medium through which that revelation comes to us, and the rule of faith by which we are enabled to determine what is, and what is not, revealed. A place for authority to step in, when these preliminary investigations are over, and say "Now, be careful, for you are out of your depth here. How many Persons subsist in the Unity of the Divine Nature, what value and what power underlies the mystery of sacramental worship, how Divine Grace acts upon the human will--these and a hundred other questions are questions which your human reason cannot investigate for itself, and upon which it can pronounce no sentence, since it moves in the natural not in the supernatural order. At this point, then, you must begin to believe by hearsay; from this point onwards you must ask, not to be convinced, but to be taught." Is it really so illogical in us, to fix the point at which our private judgment is no longer of any service? Are we really more inconsistent than the bather who steps out cautiously through the shallow water and then, when it is breast-high, spreads out his hands to swim?
--Msgr Ronald Knox, The Belief of Catholics, 1927