This post is pretty much for my own clarification. It’s pretty long, so you don’t have to read the whole thing. If it interests you at all, you can scroll down and read my summary at the end.
Catholics often criticize Protestants for exercising their own absolute right to private judgement. Protestants retort by saying that Catholics do the same thing. This objection is known as the Tu Quoque. It is when the person defends against a criticism by saying, “You do it too, so it’s OK.” I’ve intuited that this retort is wrong but wasn’t very clear on why.
I came across a post at Called to Communion that addresses the subject. I got more out of the comments than the original post. If you are so inclined, read the post and the comments. There is a lot of good stuff there, but the entire comment thread is extremely long.
One of the commentors said:
… the object of Catholic assent is fundamentally different in kind from the object of Protestant assent, even if the process of inquiry leading up to the assent is otherwise very similar in form and diligence…
Later this same commentor says:

…what distinguishes Catholicism from Protestantism is the sort of assent each involves. Since the Protestant recognizes no individual or ecclesial authority as infallible under any conditions, even when he considers Scripture inerrant (which not all Protestants do), the Protestant must inevitably regard as provisional any assent he might render to doctrinal statements, whether those statements are offered as mere expositions of Scripture or go beyond that. If he considers Scripture inerrant, he will of course say that his assent to the truths contained in Scripture is absolute not provisional. But to the question what the truths we can extract from Scripture actually mean or imply for doctrinal purposes, he can answer only by citing expositions and interpretations that represent his own or others’ opinions. Affirming that Scripture is inerrant, therefore, affords the Protestant as such no basis whatsoever for saying that we know what, exactly, God is revealing to us through Scripture in a manner that can be expressed by doctrinal statements. He might of course glean, from his own reading of Scripture and the work of his preferred scholars, a pretty fair idea of what the human authors of Scripture intended by their words. But given his rejection of infallible interpretive authority, the Protestant leaves himself in no position to distinguish reliably between de fide doctrines—i.e., the doctrines to which God calls for our assent—and the theological views of both authors and interpreters. Hence the Protestant as such has no way in principle to distinguish clearly the assent of faith, which is a divine gift involving assent to statements made with divine authority, from mere human opinions about what various “sources,” primarily Scripture, actually transmit to us as divine revelation.
This means, among other things, that the Protestant sees something called “the Church” in a fundamentally different way from Catholics. Given how he conceives assent to divine truth, the Protestant cannot see something called “the Church” as a sure guide to discerning it. Since “the Church” is fallible under all conditions, her orthodoxy is to be judged by what this-or-that person or group takes to be the doctrinally correct interpretation of Scripture (and other sources too, on some accounts), rather than vice-versa. Ultimately, the Protestant’s assent involves submission not to “the Church” but to himself as his most reliable guide to discerning divine revelation. “The Church,” from this point of view, is simply the set of people who ascribe to the “correct” interpretation of the sources, where what’s “correct” is what the individual believer provisionally accepts as such. The claims of this-or-that church to a certain kind of authority thus form no part of the deposit of faith; rather, what counts as “the Church” depends on its conformity to the deposit of faith, when said deposit is understood in a manner logically independent of any ecclesial claims to authority. Thus “the Church” is not strictly necessary for knowing Truth himself. It might be educationally useful for some, and is certainly pastorally useful for many. But that’s about it. In principle, it’s quite possible to read the Bible alone in a room and thereby learn all that God wants us to know for our salvation. Of course that sort of thing yields a variety of opinions whose holders like to call “doctrines” given by the Holy Spirit. Many of those opinions are, of course, mutually incompatible. That’s why we have more Protestant denominations and sects than anybody, including Protestants themselves, can agree on how to count.
When the Catholic, on the other hand, makes his assent of faith, he is among other things assenting to the claims made by a visible, historically continuous body that it is the Body of Christ on earth, authorized by him as her Head to teach in his name and thus, when speaking with her full authority, protected by his Spirit from requiring belief in propositions that are false. Accordingly, the Catholic does not, because as such he cannot, claim to know the deposit of faith in a manner logically independent of the claims the Church makes for herself. He does not, because he cannot, claim to know the “true doctrine” from the sources without depending on the authoritative certification of the sources as such by the Church, and the authoritative interpretations thereof by the Church. Thus for the Catholic, faith in the risen Christ, acceptance of the Bible as the Word of God, and faith in the teaching of the Church as that of the Body of Christ are logically inseparable from each other. And so the Catholic does not judge the orthodoxy of the Church; rather, he submits to the Church as, among other things, the judge of his orthodoxy.
We are now in a position to address the question why the Catholic mode of assent

should be preferred to the Protestant’s. But we cannot settle that question just by learning the historical dataset and deciding, with our own human judgment, whether it best supports Catholicism or some version of Protestantism. Most people are in no position to take in all the relevant data, and even those who are in such a position disagree on how to interpret it for the purpose at hand. From a historical point of view, the question is which hermeneutical paradigm (HP) to adopt for the purpose of interpreting the data: the Catholic, or some Protestant version.
Now the question which HP to adopt cannot be answered by appeal to the dataset itself, for the question is precisely which manner of interpreting the data is preferable. The question can only be answered, I believe, by asking ourselves which HP is better suited to distinguishing the propositionally expressible content of divine revelation itself—assuming there is such a thing as divine revelation—from mere theological opinions, and thus to facilitating the assent of faith as distinct from that of opinion. Now as you say, if Catholicism is true, the answer to that question is obvious. But if Catholicism is false, we are left only with provisional opinions. And if we are left only with provisional opinions, then we have no reliable way to distinguish from human opinion that which God actually wants us to believe.
Later, he says:
… once the assent of faith in the Catholic Church is freely made in light of such an opinion, one cannot see oneself as assenting merely to an interpretation, as if it were just one legitimate interpretation among others incompatible with it. For what one is assenting to is either altogether and perniciously false, or divine authority itself. If one doesn’t see that, then one has not yet chosen to make the assent of Catholic faith.
Much later, the author of the original post writes:
… just because one initially uses one’s interpretation of Scripture, tradition and history to find something, it does not follow that one retains ultimate interpretive authority. Whether one retains ultimate interpretive authority depends on the nature of what one finds.
My summary:
- The process of interpretive inquiry leading up to assent is the same or very similar between Catholics and Protestants.
- The objects of assent between Catholics and Protestants are very different. This is the reason the Tu Quoque objection does not apply to Catholics–the two groups are not doing the same things with the objects of their assent.
- Object of Protestant assent: Protestants assent to Holy Scripture as the Word of God, and their own ability to understand it according to God’s will. “The Church” is the set of people who ascribe to the doctrines and dogmas that the individual Protestant believes to be the correct interpretations of the Scriptures. No interpretation of Scripture has divine authority, not even the inquirer’s own interpretation. No creed or confession is binding. The Holy Scriptures are of divine origin but interpretations of them are not.
- Object of Catholic assent: the Church founded by Jesus Christ, visible, historically continuous, protected by the Holy Spirit from requiring belief in propositions that are false. Today’s Catholic bishops are the direct successors of the Apostles. The Catholic conforms his beliefs to what the Church teaches. The nature of what he found means that he is no longer the final interpreter–he no longer submits only when he agrees. He has found something objective, outside of himself, of divine origin.
- If Catholicism is true: then the inquirer has found the true Church and can absolutely rely upon her in matters of faith and morals.
- If Catholicism is false: then the inquirer has fallible opinions about the meaning of Scripture (including his own), and has no objectively sure way to know God’s will regarding the correct interpretation of Scripture. He can’t be certain of the difference between faith and opinion.
Another commentor remarked that going from Protestant to Catholic was like the difference between dating and marriage. I have often felt the same way. There was certain surrender that happened when I became Catholic.
This is all to say that Catholics are not subject to the Tu Quoque objection. This is because Catholics and Protestants find something different at the end of our respective inquiries. Because we find something different, Catholics don’t “do it too.” The “it” being “retain personal and final interpretive authority over the Scriptures.”
(This post is not a defense of the Catholic magisterium, apostolic succession, etc. It only shows how Catholics aren’t subject to the Tu Quoque objection.)
Image credit: Holger Weinandt