Plantinga’s ontological argument, take three

Rather than respond directly to comments on my previous post, I’m rewriting it, taking the issue “from the top” so to speak. The last four paragraphs are what I’d most like people to read and comment on, but the earlier parts are changed quite a bit too by adding a discussion of William Lane Craig.

I’ll begin with what William Lane Craig says about Plantinga’s argument in the third edition of his book Reasonable Faith (just because I’m writing this with a view towards including it in the book, which will have a whole chapter on Craig):

Now in his version of the argument, Plantinga conceives of God as a being which is “maximally excellent” in every possible world. Plantinga takes maximal excellence to entail such excellent-making properties as omniscience, omnipotence, and moral perfection. A being which has maximal excellence in every possible world would have what Plantinga calls “maximal greatness”…

1) It is possible that a maximally great being exists.
2) If it is possible that a maximally great being exists, then a maximally great being exists in some possible world.
3) If a maximally great being exists in some possible world, then it exists in every possible world.
4) If a maximally great being exists in every possible world, then it exists in the actual world.
5) If a maximally great being exists in the actual world, then a maximally great being exists.
6) Therefore, a maximally great being exists.

In my view, the jargon Plantinga uses in this argument is needlessly confusing. Instead of talking about “maximal excellence” and “maximal greatness,” he could just define God as “an omnipotent, omniscient, morally perfect, necessarily existent being.” Similarly, there’s no need to invoke possible world talk, we can state the argument talking just about possibility and necessity (where “necessary” just means “couldn’t possibly be otherwise”). That condenses the argument to:

1) It is possible that God exists. (Craig’s premise 1)
2) If it is possible that God exists, then it is necessary that God exists. (Craig’s premise 3)
3) If it is necessary that God exists, God exists. (Craig’s premise 4)
4) Therefore, God exists.

Working backwards: (3) is obvious once you know what “necessary” means. If God couldn’t possibly have not existed, then of course God exists. Premise (2) is supposed to come from a combination of two things: the definition of God as a being who exists necessarily, and the S5 axioms of modal logic.

Some people are going to object about simply defining God as a necessary being. However, among atheist philosophers, the attitude generally seems to be, “Oh, theists can define ‘God’ however they want. For example, if they want to define ‘God’ as ‘the greatest possible being,’ they can do that.”

Now, after granting theists their definition of God as a starting point, some atheist philosophers, Michael Martin for example, might argue that the concept of a greatest possible being is incoherent, or incompatible with other things commonly believed of God, but the point of that sort of attack isn’t to show that it’s wrong to define God that way, it’s to show that if we define God that way, then God can’t possibly exist.

In fact, in the philosophy world it seems to be generally regarded as OK to just announce that you’re going to use some word to mean such-and-such. As long as it isn’t needlessly confusing, and you don’t equivocate between two different meanings of a word, you can define words however you want. So I think most philosophers are going to give Plantinga the OK on the first piece of support for premise two.

Now the other piece: in a system of formal logic, axioms are things you’re allowed to just assume when working within the system. So for example, when I was in graduate school, the homework problems for my formal logic class generally involved proving some theorem or other. If we were working within a particular system of logic, we were allowed to have a step in our proofs be writing down an axiom with a note indicating “this is an axiom.”

The S5 axioms for modal logic–the logic of possibility and necessity–have the important consequence that if something is possibly necessarily true is necessarily true. This, when combined with the definition of God as necessarily existing, is where the otherwise bizarre-looking premise (2) of my restatement of Plantinga’s argument comes from. Philosophers have disagreed on which axioms are the right axioms to use when doing modal logic. And I don’t know of any decisive argument to show that the S5 axioms are the right axioms.

However, my understanding is that most philosophers nowadays accept the S5 axioms, and Plantinga’s key claim seems plausible enough to me. To say that what’s possibly necessarily true is necessarily true is to say that it makes no sense to think the following: “well, this could be false, but it could also be such that it couldn’t possibly be false.” And I don’t see how that makes any sense, if we’re talking about genuine possibility (what Plantinga calls “broadly logical possibility”) rather than possibility-for-all-I-know (often called “epistemic possibility,” from the Greek word for knowledge).

At this point, Plantinga’s argument may look pretty good. He’s got the first two key claims, and of course it’s at least possible that God exists, right? Not so fast. Once you accept the S5 axioms, it becomes completely crazy to think you can just assume things are possible. Or at least, it becomes completely crazy to assume things are possibly necessary. This is because S5 allows for Plantinga-style arguments for any purported necessary truth. The fact that the argument involves God isn’t actually an important feature of the argument.

So for example, philosophers generally claim that mathematical truths are, if true, necessarily true. Two plus two not only equals four, it could not possibly equal anything other than four. Because of this, if you accept S5 and also are willing to just assume a given mathematical claim is possibly true, you can “prove” that mathematical claim through a Plantinga-style argument.

For example: the Goldbach conjecture is an oft-cited example of a mathematical claim that nobody has been able to prove or disprove. If you accept the S5 axioms, and also assume that the Goldbach conjecture is possibly true, you can reason like this: “Possibly the Goldbach conjecture is true. But it is if true, necessarily true. So possibly the Goldbach conjecture is necessarily true. Therefore, by S5, the Goldbach conjecture is true!” Obviously, it is absurd to think you can prove the Goldbach conjecture that way.

It’s important to be clear on where the absurdity comes from. It does not come from the S5 axioms alone, nor does it come solely from assuming that the Goldbach conjecture is possibly true. Rather, it comes from the combination of those two things. S5 and taking possible necessities for granted are two things that do not go well together. My inclination is to accept S5, but reject assuming such possibilities. (Note that you could claim that while it’s not okay to assume mathematical claims are possible, but is okay to assume God is possible. But why would you think that?)

It’s also important to emphasize the distinction between genuine (“broadly logical”) possibility and (“epistemic”) possibility-for-all-we-know. I suspect that’s where part of the appeal of just assuming possibilities comes from. The Goldbach conjecture might be true for all we know, but it might be false for all we know. In that sense, both are possibilities. But, according to the conventional wisdom about mathematics, if the Goldbach conjecture turns out to be true, there was never a genuine possibility of it being false. There was only “possibility for all we knew.”

Craig does not deal with the Goldbach Conjecture objection, but he does deal with the objection that you might use a Plantinga-style argument to prove the existence of “a necessarily existent lion.” In response, Craig argues that “does not seem even remotely incoherent,” which means we should think it is possible that God exists. In contrast:

The idea of something like a necessarily existent lion also seems incoherent. For as a necessary being, such a beast would have to exist in every possible world we can conceive. But any animal which could exist in a possible world in which the universe is composed wholly of a singularity of infinite spacetime curvature, density, and temperature just is not a lion.

But it makes just as much sense to argue that we can conceive of a world containing only physical objects is not a world with a god in it, therefore it is possible that God does not exist. This, incidentally, entails that if God is defined as existing necessarily, we have just proved that God does not exist. Incidentally, this makes me think that theists ought not define God as existing necessarily, because it makes the existence of God too easy to attack.

To see that this is a problem with the ontological argument, though, you do not have to agree with the argument that God is possibly nonexistent, and therefore nonexistent. You need only think we have no more business assuming a possibly necessarily existent God than we do assuming a possibly necessarily existent lion.

Now unlike Craig, Plantinga is not so crazy as to claim that his argument actually proves the existence of God, or to insist people must grant his assumption that God is possible. Instead, he says, of ontological arguments:

They cannot, perhaps, be said to prove or establish their conclusion. But since it is rational to accept their central premiss, they do show that it is rational to accept that conclusion.

But again, by analogy with mathematics, we can see that this is a silly way to argue.

Imagine two mathematicians, Alice and Bob, arguing over whether it’s reasonable to believe the Goldbach conjecture. Alice argues that the Goldbach conjecture is unproven, and we should not believe unproven mathematical claims. Bob concedes that it is unproven, but says the Goldbach conjecture seems true to him, and it’s reasonable for him to believe it on that basis.

Now, you may agree with Alice here, or you may agree with Bob, but imagine Bob tried to strengthen his position by saying, “Well, surely you agree that it’s at least reasonable for me to believe that the Goldbach conjecture is possibly true. But if I believe the Goldbach conjecture is possibly true, S5 allows me to infer that it is true. So it’s reasonable for me to believe the Goldbach conjecture.” This is a silly argument. Even if you think Bob is reasonable to believe the Goldbach conjecture, this can’t be the reason why.

Once again, we need to be very clear on what the problem is. The problem is not necessarily that it is unreasonable to think that the Goldbach conjecture is possibly true. Maybe Bob is right about that. The problem, instead, is that Bob cannot expect Alice to agree. Given that Alice thinks it is unreasonable to accept the Goldbach conjecture, she probably will not think it is reasonable to believe the Goldbach conjecture is possibly true, especially if she accepts the S5 modal axioms. Bob’s argument is, if not quite circular, an example of an argument that would be bad even if it were deductively sound.

So, not only does Plantinga’s argument fail to prove the existence of God, it fails even in Plantinga’s stated goal of showing that belief in God is reasonable. Nor, I think is it especially insightful in any other way. Plantinga did not invent the S5 axioms, he was not the first person to suggest they are the right modal axioms, and I do not think he provided any decisive argument for them (I don’t think such a decisive argument exists.)

The argument could work as a clever illustration of the S5 axioms–the sort of thing a professor might mention to his student while explaining modal logic, or that might end up on a whiteboard of a grad student lounge as a joke. But it does nothing whatsoever to establish the intellectual respectability of theism.

On a semi-related note: Anyone willing to buy me Plantinga’s new book so I can review it? Link to my Amazon wishlist here. Based on Michael Ruse’s review, I expect that the book will be terrible, but terrible in ways that I feel a need to be able to comment on first-hand. That means reading it, yet I don’t want to spend my own money on something I’m so sure will be terrible. So who’s willing to help me out?

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19 Comments.

  1. So I have little to no formal training in philosophy, so I might not be getting something here. But what’s up with offering up a deductive argument you don’t even believe in? It’s my understanding that deductive arguments, unlike the inductive kind, are either airtight, and thus compelling to all rational beings, or wholly false, and therefore should not convince anyone of anything. With this in mind, Plantinga’s wishy-washy semi-endorsement seems disingenuous in the extreme. Is there something that I’m not getting? Or is this defense really that weak?

  2. @Caio, my comment from Facebook might help clarify:

    “ … imagine Bob tried to strengthen his position by saying … This is
    a silly argument. Even if you think Bob is reasonable to believe
    the Goldbach conjecture, this can’t be the reason why.”

    I don’t this is a fully accurate parallel to what Plantinga is trying
    to do. His first point is simply to lay out the validity of the logic.
    His second, I think, could be summarized roughly by saying
    “it is epistemically possible that (and therefore reasonable
    to think that) the existence of God is logically possible,
    therefore it is reasonable to think that God exists.”

    You point out that “ … The problem … is that Bob cannot expect Alice to agree.” But Plantinga explicitly notes this and already agrees: “it must be conceded that not everyone who understands and reflects on its central premise — that the existence of a maximally great being is possible — will accept it. Still, it is evident, I think, that there is nothing contrary to reason or irrational in accepting this premise.”

    That’s quite impeccably modest, I’d say. You seem to take Plantinga as implying that he has established that theism is more rational than the alternatives, or something, when he claims to have established that accepting theism is “reasonable.” But all he means here is that it’s epistemically reasonable for someone to accept theism. He doesn’t, as you seem to think, anywhere even imply that the epistemic possibility of God’s existence is what proves it. The logic states that God’s logically possible existence would establish his actual existence, and then Plantinga—in just a couple of sentences, addressing it as an aside because it isn’t the aim of the paper to do anything but lay out the logic for a working ontological argument—suggests that since there is nothing clearly “contrary to reason” in accepting that his logically possible existence (i.e., it is epistemically possible that his existence is logically possible), it is neither “contrary to reason” to accept that he exists. It’s about epistemic justification.

    Now, this would be useless in the debate over Goldbach’s conjecture presumably because mathematical debates don’t reach such levels
    of vitriol as ones over religion, and presumably there would be
    no need for someone accepting Goldbach’s conjecture to say
    ‘whoah, look, I’m within my epistemic rights here.’ If it did,
    then who knows; maybe we’d end up needing that. But this
    isn’t meant to prove any kind of conclusion one way or another.

    Essentially, what it does is this: it shifts the burden of proof, from weighing solely on the theist to balancing somewhere in the middle. If an atheist comes to the theist demanding that he justify his belief because he bears the sole burden of proof, the theist can say, “Here’s the logic, and here I see no reason not to accept the first premise. If you want to reject it, fine; I expect yiou to. But if you want to tell me that my own belief is irrational, you bear the burden of explaining what is irrational about accepting that premise.”

    He doesn’t deny that there is plenty of room for debating that premise, either. He also explicitly says, “The only question of
    interest, it seems to me, is whether its main premise… is true.”

    I think Plantinga’s argument does that much, at least.
    So I agree that it’s at least “halfway good.” At this point
    our divergence is respectable, but it still seems you’re somewhat misconstruing his aims. Most of the people arguing that Plantinga confuses epistemic and logical possibility, I think, fail to realize
    that Plantinga keeps the two perfectly straight, and they’re the
    ones confusing them in his argument and thus missing his point.
    4 minutes ago · Like

    Ashtad Bin Sayyif ‎:
    In other words, you’re right that these points apply to Goldbach’s conjecture as well—but not only is that not incompatible with Plantinga’s point or aims, he could just as easily have used
    this example to demonstrate them, by saying “In the case of
    the conjecture, neither party bears any particularly higher burden
    of proof than the other. And this is the dialectical situation which
    I claim that this argument establishes theism, also, to be in.”

  3. Caio- Plantinga’s rhetorical structure seems to be something like this:

    1. If you accept his definition of God as a modally necessary being, and

    2. If you believe that its possible that such a God could exist,

    3. Then you can just go ahead and make the jump to believing that such a God actually DOES exist, because to say that a necessary being possibly exists is to say that it actually exists.

    My problem with this is that 3 doesn’t add any useful insight. You have no business accepting (2) if you don’t already believe (3).

    You can illustrate this by just reversing it:

    1. If you accept his definition of God as a modally necessary being, and

    2. If you believe that its possible that such a God might not exist,

    3. Then you can just go ahead and make the jump to the strongest form of positive atheism.

    Or maybe this is a better way to explain my problem…

    Plantinga’s argument, in its rhetorical form, is a deductive argument with only one premises. And that just doesn’t fly.

    The definition of God isn’t a premise, its just clarifying terms.

    The rules of s5 modal logic aren’t premises, again, they’re just definitions of terms.

    The only actual premise, the only statement that’s about the actual state of the world, is the claim that it is “possible” that “God,” as “possible” and “God” are defined, exists.

    The conclusion doesn’t come from the combination of any facts about the world. It comes from the simple application of a set of definitions to the claim “it is possible that God exists.”

    Which means it hasn’t got any working parts, so to speak. Its not even circular, because its just a one dimensional point.

  4. CRAIG
    For as a necessary being, such a beast would have to exist in every possible world we can conceive. But any animal which could exist in a possible world in which the universe is composed wholly of a singularity of infinite spacetime curvature, density, and temperature just is not a lion.

    CARR
    For as a necessary being, such a beast would have to exist in every possible world we can conceive. But any god which could exist in a possible world in which the universe is composed wholly of pure evil, unalloyed by any good, with infinite hatred and malice just is not a lion.

    Did I say lion? I meant to edit it to say god….

    But looking at it, I find Craig’s demolition of necessarily existent lions to work equally well for necessarily existent lions, unicorns and gods.

  5. Ashtad, could you look at Graham Oppy’s comments on Plantinga’s argument in Oppy’s SEP article and tell me what you think?

    I ask this as a check on the clarity of my writing. I take it that I am making points very similar to Oppy’s points. If you read Oppy and think he’s making different points than I am, that suggests I may just be failing to write clearly. However, if you find Oppy problematic for the same reasons you find what I’m saying problematic, that suggests the source of our disagreement lies elsewhere.

  6. There are minor differences, but you do both make the same point (which I’m disputing) that the argument doesn’t show the rationality of theism even for the theist just because the atheist can’t be expected to agree with the first premise.

    We don’t expect (e.g.) committed Biblical inerrantists to agree with the claim, ‘if God exists then gratuitous suffering is unlikely’ (they believe and are content with the fact that God has commanded genocide at times through history); and yet the argument from evil carries a great deal of weight anyway—for one thing, it places a burden on the theist to present a plausible theodicy should he wish to declare the atheist’s denial of god unreasonable. And if a theist has good grounds for accepting Biblical inerrancy that the atheist does not, it could be rational for him to reject the argument from evil even while the atheist accepts it. This is, again, why I keep saying the point of the argument is about epistemic justification; about what it is rational for different people to accept. Declaring the acceptance of theism rational on the basis of this argument is not the same thing as declaring atheism irrational in light of it.

    Now, I’d actually say that you argue for the point (which I reject) here much better than Oppy does; the analogy you make (with Goldbach’s conjecture) is actually relevant. Oppy declares that, with the “Either God exists, or 2+2=5” argument, “no one thinks that that argument shows [ … that it is rational to accept the conclusion of the argument … [s]ince it is rational to accept the premise (and the argument is valid)….]” But then he does nothing here to defend or even make explicit the insinuation that “Either God exists, or 2+2=5” is rationally on par with “it is (logically) possible that God exists.” I think it’s obvious that the latter is reasonable in a way that the former is not: The former claim could be defended or refuted in sub–argument, while the latter could not; many people including atheists find the former prima facie plausible; and the logical connection between God’s possibility and actuality can be (and is) elaborated in a way that the supposed logical connection between God’s existence and 2+2 being equal to 5 could not.

  7. Ashtad: I’m making a slightly different point.

    The statement “it is logically possible that God exists” is not rational to accept (given the definitions used for God and for logically possible) unless you can first prove that its rational to believe that God (as so defined) actually does exist.

    And I think you’re… falling for the sucker position in this rhetorical nonsense. Rhetorically, this argument relies heavily on elision between different definitions of “possible” and different definitions of “God.” You write,

    “many people including atheists find the former prima facie plausible;”

    but for the definitions of “possible” and “God” that Plantinga uses, you’re almost certainly wrong. Most people don’t even know modal logic, and the concept of a necessary being in the modal sense isn’t the same as the concept of a necessary being in the classical sense (unsurprising as they didn’t have modal reasoning then). Your statement makes sense only if you’ve internalized the elisions commonly used in presenting this argument.

  8. To further comment (though it doesnt bear directly on the point, it might help make me clearer):

    “If, for example, I doubt that it is rational to accept the claim that God exists, then you can be quite sure that I will doubt that it is rational to accept the claim that either 2+2=5 or God exists.”

    But nearly everyone will deny the rationality of the claim that either 2+2=5 or God exists; including theists, because there is just no plausible logical connection here. But in Plantinga the logical connection between God’s possibility and actuality has been elaborated. And an atheist could very well easily accept the prior possibility of God’s existence while concluding on a posteriori grounds (divine hiddenness, argument from evil, etc.) that our world happens to have been one created by such a God. So the comparison fails.

    “ … the very same point can be made about Plantinga’s argument: anyone … who understands the … argument, and who has doubts about the claim that there is an entity which possesses maximal greatness, will have exactly the same doubts about the claim that there is a possible world in which there is an entity which possesses maximal greatness.”

    Probably not >exactly the same doubts, no. If they doubt that it happens to be the case that our world was created by a maximal being, then they wouldn’t have the same doubts about the logical possibility of such a being existing. And if their atheism was always motivated by a denial of even the possibility of God existing, then we can move on to debating the competing reasons to deny or accept that possibility in the context of Plantinga’s argument. So again, the comparison fails.

    In sum, however, the basic point I’m rejecting is that the argument doesn’t even show the rationality of theism for the theist (which is what I take “halfway good” to mean) just because the atheist might be expected not to agree with the premise. (Which, once again, he wouldn’t have to. I take the fact that so many atheists seriously consider the arguments from divine hiddenness, evil, etc. as evidence they themselves accept the logical possibility of God’s existence, and thus want to compare the features of our world with the features they expect it would have if that possibility were actual in order to determine the likelihood of theism.)

  9. @Ashtad: I think we agree on what Plantinga is up to. You think I’m attributing something to Plantinga I never meant to attribute to him, suggestions on how I could have made that clearer would be appreciated.

    On shifting the burden of proof:

    You imagine the theist saying: “But if you want to tell me that my own belief is irrational, you bear the burden of explaining what is irrational about accepting that premise.”

    But what work is Plantinga’s ontological argument doing here? Why not just say if you want to tell me that my own belief [in the existence of God, presumably] is irrational, you bear the burden of explaining what is irrational about accepting that belief.” Why is your way supposed to be any more compelling?

    I mean, if someone thinks atheism is the only rational view, since atheism entails that God does not exist necessarily, they’re going to think “God does not exist necessarily” is the only rational view there too.

    On the problem of evil comparison, in my view it’s possible to state the problem of evil in a way that will appeal even to many theists, I don’t think the reverse can be said of Plantinga’s ontological argument.

  10. “I think we agree on what Plantinga is up to. You think I’m attributing something to Plantinga I never meant to attribute to him, suggestions on how I could have made that clearer would be appreciated.”

    Well, when either you or Oppy give a statement of atheistic rejection of the argument and then say that it isn’t good at all, it sounds like the argument is being taken as some sort of attempted proof. e.g. After describing why an atheist isn’t going to find the argument compelling, you immediately say: “So, … it fails even in Plantinga’s stated goal of showing that belief in God is reasonable.“ Oppy, of course, does the same thing. If the argument fails in that goal, it doesn’t fail for those reasons. So stating “therefore, the argument fails even in this goal” immediately after giving those reasons makes it seem as though you think it fails in that goal for those reasons.

    But, I dont think this (“if someone thinks atheism is the only rational view, since atheism entails that God does not exist necessarily, they’re going to think “God does not exist necessarily” is the only rational view there too.”) is necessarily true: atheism per se doesn’t on the face of it entail to most that God’s nonexistence is necessary. Plenty of atheists think either that atheism is the default position just because it is a negative claim, or that evidence (hiddenness, evil) makes it contingently so that God very probably does not exist, although he could have (or even that he still might however dismal that probability is).

    So “what work is Plantinga’s ontological argument doing here?” At least for these sorts of atheists, the burden shifts such that they now should have to show why the existence of God is necessarily impossible if they want to attack the theist; and that’s a stronger claim than either placing the burden square on the theist since atheism is a ‘mere negative claim’ or merely considering theism contingently improbable for inferential reasons.

  11. I think this finally nails down your objection to the argument, and I agree with this (and so would Plantinga I think).

    And this is why I think Plantinga would (correctly) point out that the essence of the debate should then turn to exploring the issue of whether or not his conception of a maximally great being is coherent or not. This is obviously a centuries old debate, especially the debates over god’s attributes.

    “Now, you may agree with Alice here, or you may agree with Bob, but imagine Bob tried to strengthen his position by saying, “Well, surely you agree that it’s at least reasonable for me to believe that the Goldbach conjecture is possibly true. But if I believe the Goldbach conjecture is possibly true, S5 allows me to infer that it is true. So it’s reasonable for me to believe the Goldbach conjecture.” This is a silly argument. Even if you think Bob is reasonable to believe the Goldbach conjecture, this can’t be the reason why.”

    I don’t think this is a silly argument at all. The only response to this argument would be to take issue with “surely you agree that it’s at least rational to think the conjecture is possibly true.” That’s the only line of attack Alice could have

    I think there’s a much larger issue looming over this post that most people haven’t seen, and that’s the subjectivity of rationality. What is Plantinga to do if he can’t give a water-tight proof for the coherence of God? He has argued for it at length. If he fails to demonstrate it to your satisfaction then it isn’t clear what else there is for him to do. You’ve been following Ashtad’s posts on Philosophy of Mind. on Facebook, it reminds me of Searle’s exchange with Dennett:

    “If it consciously seems to me that I am conscious, then I am conscious. It is not a matter of “intuitions,” of something I feel inclined to say. Nor is it a matter of methodology. Rather it is just a plain fact about me—and every other normal human being—that we have sensations and other sorts of conscious states.

    Now what am I to do, as a reviewer, in the face of what appears to be an obvious and self-refuting falsehood? Should I pinch the author to remind him that he is conscious? Or should I pinch myself and report the results in more detail?”

    It seems to Plantinga that, upon close scrutiny, a maximally great being is possible. It seems to Alice that either a) this is not the case, or b) this is indeterminate.

    Could it be possible that both Plantinga and Alice are rational? Is rationality mutually exclusive? If upon close reflection, Plantinga can see no reason to believe that there’s some hidden incoherence in his notion of a Maximally great being, why may he not, using S5, reaffirm to himself the rationality of his belief in God? An outside observer may then butt in and say “Excuse me sir, but…can you show me why I ought to accept that first premise?” Plantinga may try to do so, and he has, but at the end of the day, what is it to him that you remain unconvinced? He violates no epistemic duty in continuing to believe in God simply because he can’t convince *you*, and outside observer, of the truth of his intuition that maximal greatness is possible.

    Now, your blog takes the perspective of the outsider. “What if Plantinga hasn’t shown me that this concept is coherent? Then his argument doesn’t work.” I don’t think it shows the argument doesn’t work, it merely shows that, again, either a) premise 1 is indeterminate, in which case we should remain agnostic on this issue, or b) that you think premise 1 is false, in which case the argument is unsound. But you haven’t pressed for b), you seem to continue pressing for a), which seems to me to warrant the conclusion:

    “If you fail to demonstrate the coherence and possibility of the concept of maximal greatness, then your argument shouldn’t convince *me* that your belief is rational.”

    But, this is where it gets weird, because you may write a blog from Plantinga’s perspective:

    “I haven’t been able to persuade you that maximal greatness is coherent, thus I’m not rational in believing it to be true.”

    That seems false (I think).

    At any rate, I think this was mentioned in your previous post, I think the debate should focus on the first premise. That’s the only place where a worthwhile objection could be made.

  12. “The conclusion doesn’t come from the combination of any facts about the world. It comes from the simple application of a set of definitions to the claim “it is possible that God exists.”
    Which means it hasn’t got any working parts, so to speak. Its not even circular, because its just a one dimensional point.”

    This just isn’t an argument against Plantinga whatsoever. That you don’t seem to like the simplicity of it doesn’t really do much to show its falsehood.

    You have to point out what’s wrong with it, as you admit, there’s only one premise, so you ought to be prepared to argue against it. There’s no reason why an atheist ought to feel “cheated” by this, I myself see no reason to be afraid of the argument. There is ample room to argue over the characteristics of God. The coherence of omnipotence, the coherence of omnibenevolence, the coherence of the mutual existence of omniscience and free will, the coherence of a disembodied mind; all these are fertile philosophical grounds for objection. It is here that the atheist should be focused. It seems a waste of time to spend so much time pondering if this argument is “magic”, it isn’t (unless you’re a logician and are ready to jump into the debates over Modal logic, I’m not qualified to do so, I don’t know if anyone here is).

  13. “The statement “it is logically possible that God exists” is not rational to accept (given the definitions used for God and for logically possible) unless you can first prove that its rational to believe that God (as so defined) actually does exist.”

    This is an interesting point, but you failed to tell us why we should accept this. Are you saying that evidentialist natural theology (Craig, Swinburne, etc.) should take precedence over the a priori? Swinburne would certainly agree, but he’d agree because he’d suggest that God’s existence can’t be proven a priori. Your point seems to suggest that if it could, it’d need to be demonstrated on evidentialist grounds *first*. Why?

  14. After describing why an atheist isn’t going to find the argument compelling, you immediately say: “So, … it fails even in Plantinga’s stated goal of showing that belief in God is reasonable.“ Oppy, of course, does the same thing. If the argument fails in that goal, it doesn’t fail for those reasons. So stating “therefore, the argument fails even in this goal” immediately after giving those reasons makes it seem as though you think it fails in that goal for those reasons.

    Okay, so my intention was to explain not only why an atheist isn’t going to find the basic argument (about God’s existence) compelling, but also to explain why many atheists aren’t going to find the meta-argument (about the reasonableness of belief in God) compelling.

    Maybe I should have been more explicit about a few things in the Alice and Bob story: one, Alice thinks that given that the Goldbach conjecture is unproven, it’s unreasonable to believe it. Two, what Bob cannot expect Alice to agree on is that it is reasonable to believe the Goldbach conjecture is possibly true. Does that help?

    atheism per se doesn’t on the face of it entail to most that God’s nonexistence is necessary. Plenty of atheists think either that atheism is the default position just because it is a negative claim, or that evidence (hiddenness, evil) makes it contingently so that God very probably does not exist, although he could have (or even that he still might however dismal that probability is).

    Atheism entails that God does not exist necessarily.

    Now, if you define God as Plantinga does, as being a necessarily existent being, then atheism does entail that necessarily, God does not exist. You just run Plantinga’s ontological argument in reverse to get this conclusion. In fact, you can run Plantinga’s argument in reverse if it’s even possible that God does not exist. You could call this the modal ontological argument against the existence of God (MOAAEG).

    On the other hand, not all theists agree that necessary existence should be part of the definition of God. I think these theists are making the right move, dialectically speaking, because they insulate themselves from the MOAAEG.

  15. “Alice thinks that given that the Goldbach conjecture is unproven, it’s unreasonable to believe it.”

    Perhaps we could make a distinction here (as vas Fraassen does in Phil. of Science) between “belief” and “acceptance”. A thing’s being unproven does not mean that belief in it is irrational if by that we mean “contrary to reason”.

  16. Deus- It flows from the definition of “necessary.”

    In modal logic, if something is true in a possible universe, it may not be true in this universe. But if something is “necessarily true,” then its true in all universes, including this one.

    So if I have a proposition that I claim is true in a possible universe, I don’t have to prove anything to you about the statement’s truth in this universe.

    But if I have a proposition that I claim is NECESSARILY true, then in order to prove the “necessary” part, I have to prove that its not just true in one possible universe. I have to prove that is true in all possible universes. That’s what the word “necessary” means in this context. If you’ve proven that something is true in a possible universe, but you haven’t proven that its true in this universe, then you haven’t proven that its necessarily true.

    Plantinga wants to define God as a necessary being. It doesn’t matter whether there exists some possible universe where there exists a being that is like God in every way except perhaps for existing necessarily. If Plantinga wants to prove that this being has the property “exists necessarily,” then in order to do so he must prove that it exists in this universe. That’s (part of) what “exists necessarily” means.

    Trading all of this talk of “prove” out for “reasonableness” doesn’t change anything, I’m afraid.

  17. (For the record, all Andres’ stuff about the subjectivity and rationality and speaking to the argument as an ‘outsider’ got to the same point I was trying to make, and possibly more effectively.)

  18. @Andres:

    Now, your blog takes the perspective of the outsider. “What if Plantinga hasn’t shown me that this concept is coherent? Then his argument doesn’t work.” I don’t think it shows the argument doesn’t work, it merely shows that, again, either a) premise 1 is indeterminate, in which case we should remain agnostic on this issue, or b) that you think premise 1 is false, in which case the argument is unsound. But you haven’t pressed for b), you seem to continue pressing for a), which seems to me to warrant the conclusion:

    “If you fail to demonstrate the coherence and possibility of the concept of maximal greatness, then your argument shouldn’t convince *me* that your belief is rational.”

    Great, so you recognize that as my main point! And you agree with that point!

    But, this is where it gets weird, because you may write a blog from Plantinga’s perspective:

    “I haven’t been able to persuade you that maximal greatness is coherent, thus I’m not rational in believing it to be true.”

    That seems false (I think).

    Correct, except that this isn’t just true from Plantinga’s perspective! Even from my perspective, just because Plantinga’s argument doesn’t show belief in God is rational doesn’t mean it isn’t rational! They’re two separate issues!

    As I say in the Alice and Bob story, maybe Bob is rational to believe the Goldbach conjecture! That doesn’t mean appealing to S5 is a good way to show belief in the Goldbach conjecture is rational.

    (Forgive the exclamation points, it’s just that it looks like we may finally reach agreement on this, after a long period of that looking unlikely.)

  19. Huh, I guess this whole time we weren’t disagreeing at all then.

    I’m willing to grant him that his belief is rationally acceptable. That’s more than most atheists ever want to concede, I’ve no problem granting that under certain epistemic conditions, theism is rationally acceptable. I think most people aren’t in that position, thus their theism *isn’t* rational, but a few people, Plantinga included seem to me to be violating no epistemic norms.

    Good discussion though. Can’t think of anything else to add. Looking forward to reading this part of your book.