I grew up in a tradition that defined itself primarily by what it was not. We were not Catholic. This was presented less as a theological position and more as an identity marker, like being right-handed or Midwestern. The reasons offered were the usual Protestant complaints: Mary, the saints, purgatory, the papacy. But as I've gotten older and read more carefully, I've come to believe that the real fault line — the one that actually matters — is not about any particular doctrine. It is about authority itself. And on this question, I'm not sure either side has clean hands.

The Authority Problem

Here is the standard Protestant critique of Catholicism, stripped to its logical core: the Catholic Church claims an authority that no human institution can legitimately claim. It asserts that the Magisterium, guided by the Holy Spirit, can pronounce definitively on matters of faith and morals, and that these pronouncements are, under certain conditions, infallible. This is an extraordinary claim. It means that a human institution has placed itself beyond the reach of correction — at least on its most solemn declarations.

The Protestant response to this was, historically, sola scriptura: Scripture alone is the final authority. No pope, no council, no tradition can override the plain meaning of the biblical text. This sounds like a liberation from institutional authority, and in many ways it was. But it contains a subtle and devastating irony: the Protestants simply transferred the attribute of infallibility from an institution to a text.

The Catholic says: "The Church cannot err in its definitive teaching." The Protestant says: "The Bible cannot err in its original manuscripts." Both are making the same epistemological move — locating an inerrant foundation that anchors all other claims. They differ only on where that foundation sits.

This parallel runs deeper than most people in either tradition want to admit. The doctrine of biblical inerrancy, as articulated by the Chicago Statement of 1978, attributes to the biblical text essentially the same properties that Pastor Aeternus attributes to papal ex cathedra pronouncements: freedom from error, divine guidance in composition, and authority that supersedes all human judgment. The object of infallibility shifted, but the structure of the epistemological claim remained identical.

Bayesian Heresy

I find it useful to think about this in Bayesian terms. Belief updating, at its core, works like this:

You have a prior belief $P(H)$ about some hypothesis. You encounter evidence $E$. You update your belief proportionally to how well $H$ predicts $E$. This is the basic machinery of rational belief revision — and it has a crucial feature: no hypothesis is ever assigned a prior of 1 or 0. The moment you set $P(H) = 1$, no amount of counter-evidence can move you. The denominator $P(E)$ becomes irrelevant because $P(H|E)$ is always 1 regardless of $E$. You have, in mathematical terms, made your belief unfalsifiable.

This is precisely what both inerrancy doctrines do. The Catholic who assigns $P(\text{Magisterium is reliable}) = 1$ and the Protestant who assigns $P(\text{Scripture is inerrant}) = 1$ have both exited the Bayesian framework entirely. They have placed a belief beyond the reach of evidence. And the trouble is not that the beliefs are wrong — they might be right — but that the epistemic posture makes it impossible to discover if they are wrong. You have built a system that cannot learn.

The deepest form of intellectual courage is not holding controversial beliefs. It is holding all of your beliefs with appropriate uncertainty — including the ones you most desperately want to be true.

Epistemological Comparison

The structural parallels become stark when you lay them out explicitly:

The failure modes are particularly revealing. Catholicism tends toward institutional rigidity — it takes centuries to acknowledge errors (Galileo, the treatment of indigenous peoples, the abuse crisis). Protestantism tends toward fragmentation — without a central authority, every disagreement produces a new denomination. There are now over 40,000 Protestant denominations worldwide. Both failure modes are direct consequences of the authority structure each tradition adopted.

What I Actually Believe

So why am I not a Catholic? Not because of Mary or the saints or purgatory — those are interesting theological questions, but they're downstream of the real issue. I'm not a Catholic because I can't assign $P = 1$ to any human institution's claim to speak for God. But I'm also not a confident Protestant, because I can't assign $P = 1$ to any text's claim to be without error.

What I've arrived at is something more like epistemic humility as a theological method. The Bayesian framework suggests that the most rational posture is to hold all beliefs with calibrated uncertainty, updating continuously as evidence accumulates. This doesn't mean agnosticism — you can have very strong priors, even $P > 0.99$, while still leaving the door open to revision. The difference between $P = 0.99$ and $P = 1.0$ is small in magnitude but infinite in epistemological consequence.

The expected loss from holding a belief with $P = 1$ when it is actually false can be expressed as:

where $C(t)$ is the cost of uncorrected error at time $t$. When $P = 1$, you never correct, so the integral accumulates without bound. When $P < 1$, evidence can trigger correction, and the expected loss is finite. This is not just a mathematical curiosity — it is a description of how institutions and traditions actually fail. The ones that claim certainty accumulate the largest uncorrected errors.

I believe in God. I believe the Christian tradition carries profound and largely reliable witness to something true about reality. But I hold these beliefs at $P < 1$, and I think that's not a weakness but a discipline. The alternative — inerrant text or inerrant institution — is not really faith at all. It is a refusal to be wrong, dressed up in theological language.

The irony is that both traditions claim to be about trust. The Catholic trusts the Church. The Protestant trusts the Bible. But real trust — the kind that sustains a marriage, a friendship, a life — is not the absence of doubt. It is the decision to remain committed in the presence of doubt. A faith that requires $P = 1$ is not trust. It is a demand for certainty that the human condition simply cannot provide.

And that, more than any argument about transubstantiation or the filioque clause, is why I'm not a Catholic. Not because the Catholic answer is wrong, but because the Catholic question — where does infallible authority reside? — is the wrong question. The right question is: how do we live faithfully when no authority is infallible? And that question, I suspect, is one that neither Rome nor Geneva has fully reckoned with.