Thus far we have seen Peter Boghossian to be utterly inept at defining basic terms: “deepity”, “faith” and “atheism”, he’s flubbed ’em all. So it is little surprise that his incompetence continues when he attempts to define “agnosticism”. Before we consider Boghossian’s proposed definition, and the problems with it, let’s consult a few philosophical dictionaries to see how philosophers define the term.
According to the Cambridge Dictionary of Philosophy:
“Agnosticism is a form of skepticism applied to metaphysics, especially theism.”
In the Oxford Dictionary of Philosophy we read the following:
“The view that some proposition is not known and perhaps cannot be known to be true or false. The term is particularly applied to theological doctrines.”
These definitions helpfully illumine both a general and a specific sense for the term “agnosticism”. Generally speaking, agnosticism is the claim that we currently lack knowledge (or reasonable belief) about a particular subject matter or that such knowledge (or reasonable belief) is unobtainable.
Specifically, agnosticism is the claim that we currently lack knowledge (or reasonable belief) about whether God exists or not, or that knowledge (or reasonable belief) of God’s existence or non-existence is unobtainable.
For further reading see the entry on “agnosticism” in my book Christian Philosophy A-Z (Edinburgh University Press, 2006) co-authored with the philosopher Daniel Hill.
And now turning to Boghossian
As we can see in our first section, “agnosticism” is not a particularly difficult term to define, and there are many good resources available one might consult in constructing one’s own definition, including the three above-mentioned dictionaries of philosophy. This makes it all the more glaring that Boghossian’s definition should fail in such striking fashion.
And how does it fail exactly? In part 1 I will point out that by the definition of “agnostic” that Boghossian provides, one can believe God doesn’t exist — indeed one could proclaim their certainty that God doesn’t exist — and still be an agnostic. But people who believe God doesn’t exist aren’t agnostic and so the definition fails. Even worse, as I will note in part 2, Boghossian’s definition projects onto agnostics an absurd epistemological commitment which reduces agnosticism from being a serious intellectual position to a mere caricature.
And so without further ado, let’s begin by quoting Boghossian’s definition. And please note that I’ve numbered the two sentences of the definition for ease of reference:
“ Agnostics profess to not know whether or not there’s an undetectable, metaphysical entity that created the universe.  Agnostics think there’s not enough evidence to warrant belief in God, but because it’s logically possible they remain unsure of God’s existence.” (28)
One thing is clear. Boghossian is aiming to offer a definition of “agnosticism” in the specific sense rather than the general sense. And so his definition shall be assessed accordingly.
We’re about to consider the two sentences in turn, but first I should offer a quick proviso: if you want to get to the main course, skip to . If you prefer an appetizer and salad with your meal, then read  as well.
 Boghossian’s definition of “agnostic” entails that believing God doesn’t exist is consistent with being agnostic about whether God exists
According to Boghossian’s , agnostics claim not to know whether there is an undetectable metaphysical creator of the universe. This statement is typical of Boghossian’s sloppiness, for agnostics don’t merely claim not to know whether there is an undetectable metaphysical creator of the universe. They also profess not to know whether there is a detectable metaphysical creator of the universe. In other words, the property of undetectability is not a part of the agnostic’s knowledge denial, and so it is simply mistaken (and as I said, just plain sloppy) for Boghossian to include this qualification in the definition.
In fact, Boghossian’s definition is flatly wrong at this point. The object of disbelief for the agnostic isn’t “metaphysical creator of the universe”, it is “God”. This is important because it is possible to have a non-divine metaphysical creator of the universe. As theoretical physicist Michio Kaku points out, a Type III civilization (that is, a civilization that has mastered galactic energy) could potentially create a universe. (See his discussion here.) This could be sufficient to qualify the Type III civilization as a metaphysical creator of the universe, despite the fact that it isn’t God. (A Type III civilization might be sufficient to create a universe, but would it be sufficient to qualify as a metaphysical creator? So far as I can see, Boghossian’s use of the term “metaphysical” is sufficiently non-technical that it doesn’t preclude this possibility, and so if our standard is the terms provided in the book, the answer is “yes”.)
(Footnote: If you’re really thoughtful, you might be wondering how a person could reasonably believe an undetectable Type III civilization created the universe if, by definition, it can’t be detected. Here’s one way: one might infer, based on the cosmological constants in cosmic tuning, that a mind designed this universe for life. But for various reasons one might reject the idea that this mind is divine. It would follow then that this mind is evidence for an otherwise undetectable Type III civilization.)
To sum up, according to Boghossian’s first definition, a person who believed that God didn’t exist (a designation traditionally sufficient for atheism) would count as an agnostic just if this person believed an undetectable Type III civilization-creator of our universe might exist. But any definition of “agnostic” which is consistent with a person who emphatically believes God doesn’t exist being an agnostic is surely spurious. And so Boghossian’s definition should be rejected.
 Boghossian’s definition leads to epistemological absurdities
To this point Boghossian’s definition merely reflects his trademark sloppiness. The problems faced thus far could be dealt with by swapping out the tortured phrase “undetectable, metaphysical entity that created the universe” with the simple designator “God”. This solution is so simple that one wonders why Boghossian keeps buying himself trouble with his bloated, ill-focused phraseology. (Perhaps I should send him a complimentary copy of my book Christian Philosophy A-Z.)
However, things really go off the rails when we get to . To recap, at this point Boghossian claims that “Agnostics think there’s not enough evidence to warrant belief in God, but because it’s logically possible they remain unsure of God’s existence.” As I read this claim, Boghossian is imputing to the agnostic a general epistemological principle like this:
Agnostic Principle informal (APi): “Agnostics think that whenever an entity is logically possible but one lacks evidence to believe it exists, one must remain agnostic about its existence.”
Dressed up in a formal tuxedo, the principle looks a bit more fashionable:
Agnostic Principle Formal (APf): “For any entity x, if (i) it is logically possible that x exist and (ii) one lacks evidence to believe that x exists, one ought to be agnostic about whether x exists.”
And so because the agnostic is committed to the APf (or something close to it), they conclude that they must remain unsure of God’s existence because (i) “it’s logically possible” that God exist and (ii) one lacks “enough evidence to warrant belief in God.”
It is crucial at this point that readers recognize APf is a crazy principle and there is absolutely nothing to commend it. It is also crucial to recognize that agnostics don’t widely hold APf. Certainly I’ve never met any who do. Consequently, any suggestion that agnostics should be defined by adherence to such a principle — and at the very least, Boghossian seems to suggest that they do — represents a crude mischaracterization of agnosticism.
But why exactly is APf a “crazy principle”? Well consider this logical possibility:
Possibly, there is an invisible ghost the size of the Empire State Building that looks like Kevin Spacey hovering above the North Pole.
Please note that it is logically possible that this giant Spacey ghost exist and one currently lacks evidence that it exists. Consequently, according to APf, the agnostic is obliged to withhold belief in the existence or non-existence of this ghost. But surely this is a reductio ad absurdum for the APf.
The only way Boghossian can avoid imputing this absurd belief to agnostics is by claiming that they don’t really have any formal, generalizable principle that motivates their agnosticism about God in particular (as opposed to the Kevin Spacey ghost). But with no epistemological principle guiding their disbelief, it is reduced to being an irrational, arbitrary stance. Either way, Boghossian’s definition of agnosticism reduces the position to absurdity.
A word to my critics
Thus far I’ve heard one major criticism from my critics as I’ve published the various installments of this review. According to these critics, I’m nitpicking and I’m not trying to get the big picture or spirit of what Boghossian is trying to achieve. I find this response to be indefensible.
Imagine that you want to hire a person to do sign language for a special event. In order to do your due diligence, you have a person you trust who can read American sign language ready to vet the signing abilities of your candidate. And so you present a random test in which you ask the candidate to sign four English sentences with your friend watching. After the test, your friend explains to you that the person failed on each count, flubbing basic signs and yielding signed sentences which are confused, misleading, ungrammatical, or even incoherent. Would you think this failure provided sufficient ground to decline to use this person’s services? Of course. And you wouldn’t consider for a moment anybody retorting that your friend was “nitpicking” the signs if they presented a careful analysis to back up their judgments.
I’ve presented a careful analysis to back up my judgments. I’ve shown that Boghossian’s four sample definitions — deepity, faith, atheism, agnosticism — are the equivalent of confused, misleading, ungrammatical, and downright incoherent mumblings from a very confused signer. This isn’t nitpicking, and those who insist otherwise show nothing more than an inability (or refusal) to reason in good faith.