PZ Myers over at Pharyngula has just posted an image which he says succinctly explains why he is an atheist. Here is the endorsed explanation:
I'm an atheist because of one simple fact: The burden of proof lies on religion. If you propose the existence of something, you must follow the scientific method in your defense of its existence. Otherwise, I have no reason to listen to you.
Unfortunately for Myers, the indented material above is almost entirely false. These are not good reasons to be an atheist. This doesn't mean that it's irrational for Myers to be an atheist, for he presumably has plenty of other reasons as well. You can remove a single rotten beam from the foundation of a house without toppling it, so long as other beams are still in place to bear the weight.
Our first target will be the claim that the only possible defense of the existence of something is a scientific defense. This is not a claim Myers is capable of defending. He may believe it, of course. It may be one of his favorite or fundamental principles. He may accept he because he's attracted to it. He may wish it were true. But it is wholly unmotivated and obviously false.
Before we turn to obvious falsehood, observe that the theist won't accept the claim. Or at least, the smart theist shouldn't accept it. It's obviously not obviously true that no defense can possibly be offered for the existence of something science is incapable of adducing evidence for. If the atheist wants to boldly assert this unobvious claim, she'd better be willing to back it up. (Of course, she won't be backing it up with scientific evidence. But then, it's not obviously an existence claim either, so she hasn't obviously refuted her own position.) It's at least possible that some things exist which scientific methods cannot detect. Why couldn't there be an argument that shows (or provides good reason to believe) that some of these things exist?
The committed Myers-style atheist will have to here deny the possibility of defending the existence of moments of time before the big bang, and, as they are widely conceived, of numbers, properties, relations, sets, propositions, classical substances, possible worlds, and so on ... Indeed, the committed Myers-style atheist will have to reject almost all of philosophical history and most of contemporary philosophy as utter hogwash. This is dubious at best. And nor is Myers, a biologist, in any more of a position to opine with authority on philosophy than he is to opine on physics or cosmology (in the linked post he admitted he was in no position to talk much about the latter two subjects). Indeed, it's highly unlikely he's even remotely aware of some of the consequences of denying that, for example, propositions exist.
Then, of course, we run into the problem of the status of the claim Myers makes. If it's true that the only possible defense of an existence claim is by appeal to the scientific method, then it's impossible to offer a non-scientific defense of an existence claim. What is the scientific evidence that such is impossible? Pointing out that all observed non-scientific defenses of a particular existence claim have failed doesn't show that it's impossible for one to succeed. The point that Myers is making a philosophical claim about what is and isn't possible is undeniable. As such, he'd better be prepared to adduce philosophical arguments for it. But these arguments would be arguments for the conclusion that something (namely a defense or a legitimate defense of an existence claim) cannot exist. If Myers thinks those arguments can be made, then it will be hard to see how he can deny that one could argue philosophically for the conclusion that a godless universe cannot exist. Parity of reasoning bites him in the ass.
It gets worse for Myers. Much, much worse. Consider a toy example designed to show how bad things are for him. Suppose Myers postulates the existence of tables. I then remind him that, by his own lights, he must produce scientific evidence for the existence of tables. What would be this evidence be? Well, he might bang his fist on a table and holler, "Here's scientific evidence, fool!" But that's just to adduce scientific or empirical evidence that something exists there---not that what exists is a table.
We might have gotten off to a better start if we'd made Myers define what he postulated the existence of. This is a common canard amongst atheists of Myers' ilk. No doubt Myers has invoked something like it before: the theist must define the term "god" before we can scientifically assess her claim! Well, how then will Myers define the term "table"? Of course he can't do that, so let's settle for a plausible necessary condition he might offer for something's being a table and pretend we could add further conditions to get to a definition: x is a table only if x is a composite object constituted by fundamental physical particles.
Ok, so now we know more about what toy Myers will have postulated the existence of. He'll have postulated the existence of a composite object, that is, an entity that is composed of further things. But what is the scientific evidence for their being composite objects? Perhaps the fundamental physical particles don't compose anything else. Maybe they're just all buzzing around in spacetime and failing to compose a further thing? After all, it's not obvious that it's always the case that a bunch of things compose a further thing. Do you (my dear reader) and the moon compose some third thing (call it the "fusion" or "sum" of you and the moon)?
Thus if toy Myers wants to postulate the existence of a composite object (such as, plausibly, a table), he will have to adduce scientific evidence to defend his claim that the fundamental physical things (quarks or strings or whatever you want) in some area compose a further thing. But there is no current scientific evidence that toy Myers can appeal to here. Perhaps toy Myers will claim that it's the business of the scientists to determine when composition occurs. Perhaps, but then there is no guarantee they will eventually conclude that composition has occurred. Since toy Myers has no scientific evidence that composition has occurred he should maintain that his claim that a table exists is currently indefensible.
Suppose that scientists somehow discover that composition occurs whenever condition C is satisfied. This doesn't automatically secure the truth of toy Myers' claim that a table exists. For his claim to have been true, he will have to have meant by "composition" something that can plausibly be taken to occur when condition C is satisfied.
Also observe that scientists cannot stipulate that composition occurs whenever (and perhaps not only whenever) things are related like the particles that compose the table are related. That would be to stipulate into existence toy Myers' table rather than adduce any scientific evidence for its existence.
Finally, why think that there could possibly be any scientific evidence that settles the question of when composition occurs? What sort of tests could scientists run to determine whether a bunch of fundamental particles compose some further thing? What sort of tests could they run to determine whether you and Eiffel tower compose some further thing? Have fun what that, toy Myers!
And it really matters little what Myers means by "table" when he postulates the existence of a table. The story will be the same if he means anything whatsoever of substance. And if he can't tell us what he means by "table", how can we be expected to adduce scientific evidence that tables exist? (Note the parity with the common atheistic claim that we can't begin to go about verifying the theistic claim that god exists without them telling us something of substance about what god is.) But of course we know that tables exist, and we don't need scientific evidence to justifiedly believe that tables exist, to know that tables exist, or to show or prove that tables exist. So Myers is just about as off base as one can get here.
I'm going to ignore the burden of proof shifting remarks in part because they're controversial and typically unmotivated attempts to rid oneself of intellectual responsibility. Instead, we'll focus on the last point, namely, that absent being presented with scientific evidence for the existence of god, Myers has no reason to listen to you. We might interpret that in one of two ways: (i) Myers takes himself to have no reason to listen to you, or (ii) Myers has no good reason to listen to you. The first interpretation doesn't show anything of interest. Who cares whether Myers takes himself to have a reason? What matters is whether he does have a reason. So (ii) is of more interest.
Is it true that Myers has no good reason to listen to you if you don't adduce scientific evidence in favor of your claim that god exists? Well, it needn't be false. We've seen above that Myers is not in a position to rationally believe that there can be no non-scientific evidence that god exists. But if Myers had good reason to believe that all non-scientific evidence in favor of god's existence that a person would be capable of adducing would be bad or misleading evidence, then he'd have no good reason to listen to that person. But of course, Myers doesn't know that, so it's just false he has no good reason to listen. Part of the reason why Myers doesn't know that is that he isn't philosophically competent.
Nor should he be expected to be. After all, he's a biologist, not a philosopher. As such, he has not interacted with reasons for belief in god at anywhere near the level one needs to interact with them in order to have good reason to believe that all non-scientific arguments for god's existence anyone is capable of offering will be failures. To the extent that he pretends he has, he engages in what any reasonably intelligent undergraduate philosophy major with a few courses under her belt should be able to recognize as pure bluster.
To be sure, his intellectual buffoonery is currently having the effect of promoting atheistic belief. But absent more philosophically competent and intellectually honest atheists managing to reach the atheist community, it's unclear what the future of the atheist movement will look like. One suspects that, if things continue at their current pace, most atheists will hold their beliefs for no better reasons than most theists hold their own. That'll be a sad, and perhaps unavoidable, state of affairs.