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Protestant arguments for Sola Scriptura often sound airtight—but in this episode, I show how a popular version commits a subtle logical fallacy. By unpacking Dr. Gavin Ortlund’s appeal to the Bible’s unique quality of inspiration, I explain why the conclusion that the Bible is the only infallible rule for the Church doesn’t follow.
Protestant apologists often argue for Sola Scriptura like this: 1) The Bible is an infallible rule of faith. 2) There are no other infallible rules of faith. 3) Therefore, the Bible alone is our infallible rule of faith.
On the surface, this argument might sound pretty airtight. But when you dig a little deeper, some logical cracks start to show — specifically, a fallacy that many people don’t notice. So in this episode, we’re gonna unpack the argument step by step, see where it goes wrong, and why that matters for the conversation between Catholics and Protestants.
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So, one Protestant apologist who makes this argument is Dr. Gavin Ortlund. In his 2023 debate with Trent Horn, he said this:
[VIDEO]
6:37 this topic let me Dive Right In hoping you can hear me okay by stating my 6:42 Essential argument one the Bible is an infallible rule for the church two there 6:49 is no other infallible rule for the church three therefore the Bible is the only 6:54 infallible rule for the church which is the doctrine we call Sola scriptura
Ortlund published this argument in his 2024 book What It Means to Be Protestant. He also reproduced it in his video “The ULTIMATE Case for Sola Scriptura.”
Another Protestant apologist, Dr. James White, makes the same basic argument. He did so in his 2024 debate on Sola Scriptura with Jimmy Akin, though not as neatly as Ortlund. For this video, we’ll stick with Ortlund’s version because it’s easier to map out.
So, visually, it looks like this:
P1: The Bible is an infallible rule for the Church.
P2: There is no other infallible rule for the Church.
C: Therefore, the Bible is the only infallible rule for the Church (which is the doctrine of sola scriptura).
Now, how does Ortlund defend Premise 1?
He says the Bible is an infallible rule for the Church because of its nature—because it’s the speech of God. Here’s how he puts it in his debate with Trent:
[VIDEO]
[S]cripture is the speech of God through a human medium and it’s on that 11:50 basis that we speak of scripture as infallible.
He argues the same thing in his video “The ULTIMATE Case for Sola Scriptura”:
[VIDEO]
And so this is why infallibility will come into 16:39 the picture is because we say the scripture is infallible because it’s God’s speech and God is omnisient and 16:45 perfect. So God is infallible. So God’s speech is therefore infallible. And it’s on that basis that we say the scripture 16:52 cannot heir. It cannot get it wrong.
In other words, the reason Scripture is infallible is that it’s inspired. Inspiration is the theological term that describes how God moved the human authors to write Scripture in a way that God is at the same time the principal author.
Ortlund elaborates on this, again, in his debate with Trent:
[VIDEO]
[S]ola 12:41 scriptura is simply suggesting as an implication from that fact that as the Bible is unique in its nature 12:48 so it is correspondingly unique in its Authority the alternative positions such 12:54 as those of Roman Catholicism Eastern Orthodoxy Etc separate infallibility from inspiration 13:01 those positions have the burden to show why another rule of faith that is not the inspired speech of God should 13:07 nonetheless be accepted as equal in authority to the inspired speech of God
And he adds:
[VIDEO]
[A] simple way to put Sola scriptura at a 13:15 metaphysical level God is unique therefore his speech is unique that which isn’t the speech of God is 13:22 subordinate to that which is the speech of God.
Then in his closing statement, Ortlund says:
[VIDEO]
2:16:15 [T]he classic magisterial Protestant view makes a lot of sense it’s simply saying put the Bible at the top of the pyramid 2:16:20 it’s the inspired speech of God.
So, if we put that all together, Ortlund’s argument for premise 1 looks like this:
P1.1: If an authority for the Church is inspired, then it’s an infallible rule for the Church.
P1.2: The Bible is an authority for the Church that’s inspired.
P1.C: Therefore, the Bible is an infallible rule for the Church (that’s Premise 1 of his main argument).
So far, so good! But it’s when he defends Premise 2 of his main argument that the problem arises.
Recall, Premise 2 is “There’s no other infallible rule for the Church.” Here’s how Ortlund defends this premise in his debate with Trent:
[VIDEO]
[S]cripture is ontologically unique in its nature no 12:34 other rule of faith that we possess is the god-breathed spirit carried unbreakable Oracles of God
And later:
[VIDEO]
[W]hy is the 53:18 scripture more authoritative than tradition it’s because of a simple reason scripture is ontologically unique
Remember, by “ontologically unique” Ortlund means “inspired.”
Ortlund argues similarly in his “ULTIMATE Case” video:
[VIDEO]
[N]o other rule of faith that we 19:08 have today is this inspired speech of God. And so sola scriptura is going to say 19:15 go a step further and say just as the Bible is unique in its nature 19:22 so it is correspondingly unique in its authority
So what Ortlund’s really saying is: there’s no other infallible authority for the Church — like Tradition or the Magisterium — because there’s no other authority that’s inspired.
That argument can be summarized like this:
P2.1: If an authority for the Church is not inspired, then it’s not an infallible rule for the Church.
P2.2: No authority for the Church besides the Bible is inspired (i.e., Not Tradition or the magisterium)
P2.C: Therefore, there’s no other authority that is an infallible rule for the Church.
That’s logically valid on its own. But when you combine it with Ortlund’s reasoning for Premise 1 of his main argument—that’s when the logical fallacy shows up.
To see the problem, we need a short logic refresher.
A conditional statement is an “if…then…” proposition — like, “If it’s raining, then the ground is wet.”
The “if” part is called the antecedent; the “then” part is the consequent.
Now, there’s a logical fallacy called “negating the antecedent.” It happens when you deny the antecedent and then assume that automatically denies the consequent. For example:
- If it’s raining, the ground is wet.
- It’s not raining.
- Therefore, the ground is not wet.
That doesn’t follow, right? The ground could be wet for other reasons—maybe someone left the sprinkler on.
Okay, now back to Ortlund.
In defense of Premise 1 of the main argument, he argues P1.1—if an authority for the Church is inspired [the antecedent], then it’s an infallible rule for the Church [the consequent].
But when he defends premise two of the main argument—“there’s no other infallible rule for the Church,” he says in P2.1 there’s no authority for the Church besides the Bible that is inspired. That’s a negation of the antecedent in P1.1.
Ortlund then makes a conclusion based on this negation—namely, no authority besides the Bible, like Tradition or the magisterium, is an infallible rule for the Church, which is the definition of sola scriptura.
So his argument is essentially this:
P1.1: If an authority for the Church is inspired, then it’s an infallible rule for the Church.
P2.1: There’s no authority for the Church besides the Bible that is inspired (there’s the negation of the antecedent).
C: Therefore, there’s no authority besides the Bible that’s an infallible rule for the Church (there’s the conclusion with a negation of the consequent).
So Ortlund’s overall argument commits the fallacy of negating the antecedent.
Now, Ortlund, or any Protestant who makes this argument, might counter that sometimes a denial of the antecedent does necessarily entail a denial of the consequent—when the antecedent is logically identical to the consequent. For example:
P1: If bachelor, then not married.
P2: Not bachelor.
C: Therefore, not married.
So, Ortlund might push back to my charge of his argument negating the antecedent and say that “inspiration” and “infallibility” are like “bachelor” and “married”—they’re logically identical; you deny one, you deny the other.
Ortlund seems to hint at this sort of comeback in his “ULTIMATE Case” video:
[VIDEO]
And so sola scriptura is going to say 19:15 go a step further and say just as the Bible is unique in its nature 19:22 so it is correspondingly unique in its authority and the alternative positions 19:28 are going to try to separate divine speech and biblical inspiration from infallibility. Now at that point the 19:35 burden that is going to come up as we’re going to get to is okay show us what is the ground for infallibility in this 19:41 other case where you have some other onlogical entity why is this also infallible as the scripture is infallible
I think we can shoulder that burden. Like rain and wetness, inspiration and infallibility aren’t logically identical. “Inspiration” (at least when it comes to Scripture) means God is the principal author—what the human authors affirm, God affirms. So infallibility follows from inspiration, yes—but it doesn’t mean inspiration is the only way God can make something infallible.
For example, God could providentially prevent someone —like the pope or a council—from teaching error. He could arrange events so that the pope never writes the error down or publishes it with binding authority. God also could just will that the pope dies before he binds the Church to believe the error.
So there are other ways, besides inspiration, that an authority can be incapable of error—God can protect the authority. That means inspiration and infallibility are conceptually distinct.
To put it simply:
Just as the ground can be wet without it having rained, a Christian authority can be infallible without being inspired.
So even if it were true that the Bible is the only inspired authority for the Church—that which is God’s speech (to use Ortlund’s words), that wouldn’t mean it’s the only infallible authority. The pope speaking ex cathedra, or an ecumenical council defining a doctrine, could still be infallible —just not inspired.
So, even on Ortlund’s own logic, he can’t get to Sola Scriptura. To do that, he’d have to show that inspiration is the only possible basis for infallibility. But I don’t think that’s a claim he can defend, for the reasons I’ve already stated.
Now, Ortlund might try to avoid the “negating the antecedent” problem by reformulating the argument like this:
- Whatever is inspired is infallible.
- No other authority besides the Bible is inspired.
- Therefore, no other authority besides the Bible is infallible.
That looks valid — but the conclusion only follows if you add an unstated assumption:
“Only what is inspired can be infallible.”
That assumption isn’t in either premise. Without it, the argument is invalid.
And here’s why: Premise 1 says, All inspired things are infallible. This tells us that inspiration is sufficient for infallibility.
The conclusion assumes the claim: Only inspired things are infallible. This claims that inspiration is necessary for infallibility.
But you can’t move from “All As are B” to “Only As are B” without an additional premise. That’s a fallacy of illicit conversion (or more generally, a form of the undistributed middle fallacy —where the middle term isn’t properly distributed).
Here’s an example.
- All cats are mammals.
- All dogs are mammals.
- ∴ All dogs are cats.
The argument is invalid because the middle term (“mammals”) is not distributed — meaning, it doesn’t refer to all mammals in either premise. Both premises say only that cats and dogs belong within the class of mammals, not that they’re identical to the entire class.
So while cats and dogs share a common category (“mammals”), that doesn’t make them the same. The reasoning fails to connect the two properly — just like the “inspired/infallible” argument does.
In the “inspired/infallible” argument, the middle term—“inspiration”—isn’t distributed. It only shows that “inspired” things belong within the category of infallible authority. But it doesn’t show they are the same.
To distribute “inspiration” properly and make the reasoning valid, Ortlund would need to add: “Only what is inspired can be infallible.”
But, as I’ve said already, that’s precisely what we as Catholics, along with our Orthodox brethren, would challenge — since, in our view, an authority can be infallible without being inspired in the strict sense—e.g., an ecumenical council for both Catholics and Orthodox, and the pope for Catholics.
So to sum up: this argument that Ortlund uses for Sola Scriptura, along with other Protestants, ends up committing either A) the fallacy of negating the antecedent, or B) the fallacy of undistributed middle. It assumes that because all inspired things are infallible, only inspired things can be infallible.
But that doesn’t follow because it overlooks the real distinction between inspiration (God directly speaking through a human author) and infallibility (God preventing error through divine protection).
Now, Ortlund might drop the appeal to inspiration altogether and just focus on infallibility, since his main argument as stated was valid. And that’s fine! We’re more than happy to have a conversation as to whether there’s another infallible authority besides Scripture—when we’re talking about infallibility without necessarily including the idea of inspiration.
In fact, in his “ULTIMATE Case” video, Ortlund actually seems to shift to that line of argument near the end. Although, he presents it as if it’s the same argument he started with. Here’s what he says:
[VIDEO]
Uh so 36:33 putting all of this together, we could sum it up by saying number one, 36:39 scripture is an infallible rule for the church in light of what it is and in light of what it does. Almost all 36:45 Christians historically have agreed upon that. Number two, we don’t have any other 36:51 uh rule for the church that is infallible. The major candidates would be oral apostolic traditions or ongoing 37:00 organs of infallibility within the church. But both of these are problematic. The oral apostolic 37:05 tradition has a fallible transmission process. And postappostolic infallibility just doesn’t have a 37:11 historical foundation. It’s it’s a later uh gradual accretion. So it follows that 37:17 if scripture is an infallible rule for the church and there is no other infallible rule then scripture is the 37:24 only infallible rule and that’s solos scriptural
Now notice what’s going on here. His defense for premise two—“there are no other infallible rules for the Church”—isn’t “because nothing else is inspired,” like it was in his debate with Trent and earlier in his “ULTLIMATE Case” video. Instead, he’s saying the other possible candidates for infallible authority—like oral apostolic traditions or ongoing infallible organs in the Church—just don’t hold up. He thinks oral tradition has a fallible transmission process, and the idea of post-apostolic infallible authority is just an “historical accretion.” So, at least here, he seems to be willing to allow for the possibility of an infallible authority that’s not the “speech of God.”
That’s a different argument than the one we’ve considered throughout this episode. And to be fair, this version of the argument actually avoids both of the fallacies I pointed out earlier.
So, if Ortlund wants to go with this revised version of the argument—great! Totally fair. We’d just note that, in doing so, he’ll have to retire the reasoning he used in his debate with Trent and earlier in the “ULTIMATE Case” video, for the reasons we’ve discussed here.
And I will say—Ortlund’s concerns about how oral apostolic traditions were transmitted, and about the evidence for post-apostolic infallibility in the Church, are fair game. They deserve thoughtful, careful responses from us Catholics. But… that’s a topic for another episode.
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