Someone asked me to write about Alvin Plantinga, so I’ve decided to write another explanation of who his ontological argument isn’t any good, due to not being satisfied with what I’ve previously written on this. Please tell me if the following is clear enough. If people understand it, it will appear more or less as written in the book I’m currently working on. (Current word count: 25,005 words. Yes Virginia, I am making progress on it.)
Here’s my view of the argument: Plantinga’s argument uses some esoteric ideas, and I don’t expect anyone unfamiliar with these ideas to understand what is wrong with the argument. However, I do claim that once you understand the underlying ideas, it becomes totally obvious that the argument is not a good one. Plantinga’s ontological argument does not reflect well on Plantinga as a thinker, nor does it something people should be pointing to to say “look, theism isn’t so crazy, there are sophisticated arguments for it!”
Plantinga’s ontological argument makes three key moves: (1) defining God as a necessary being, that is to say, a being who if he exists exists necessarily (2) using the S5 axioms for modal logic , which have the consequence that if something is possibly necessarily true is necessarily true and (3) assuming that it is possible that God exists.
Two key pieces of jargon here: First “necessary,” which means, “cannot possibly be otherwise.” A necessary truth is something that could not possibly be false; for God to exist necessarily is for it to be impossible that he not exist. Second, “modal,” which means “having to do with possibility and necessity.” Modal logic is the logic of possibility. In both cases, the “possibility” is supposed to be genuine possibility, not merely “possibility for all I know.”
Now, 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 I don’t that sort of attack actually depends on granting theists their definition of “God.”
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 his first step.
For the second step, 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. And if we were working within a particular system, we were allowed to have a step in our proofs be writing down an axiom with a note indicating “this is an axiom.”
Historically, 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. (Remember, we’re supposed to be talking about genuine possibility here.)
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 assume 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. But obviously it’s absurd to think you can prove anything in mathematics that way. Thus, if we accept S5, we have to refrain from assuming possibly necessities to avoid such absurdities.
Where some people might go wrong here is thinking of possibility as “possibility for all we know.” There are many claims in mathematics which we have yet to either prove or disprove. The Goldbach conjecture is an often-mentioned example (look it up on Wikipedia if you’re curious about what the Goldbach conjecture is, but the details don’t matter here). The Goldbach conjecture might be true for all we know, but it might be false for all we know. But, according to the conventional wisdom, 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.”
Now 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 that it’s reasonable to believe that it’s possible that God exists, and therefore it’s reasonable to think that God exists. 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.
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. Both of those points are totally obvious once you realize that you could give a Plantinga-style argument for any purported necessary truth, in particular truths of mathematics. If Plantinga’s argument had been something tacked to a bulletin board on a graduate student lounge as a joke, it wouldn’t have been bad as academic in-jokes go. But as a serious argument it’s worthless.
“But obviously it’s absurd to think you can prove anything in mathematics that way.”
You should elaborate a little more on this since your argument seems to strongly depend on this.
Regardless of this, I think your problem isn’t with Plantinga at all, it seems to be with the underlying logical structure of the argument. If your objection holds then there is something deeply flawed with Modal logic which isn’t Plantinga’s fault. The real “joke” here would be that so many people take modal logic seriously rather than the ontological argument since what you seem to be arguing is “hey look, if you take modal logic seriously, you could prove anything in mathematics this way, but that’s absurd.”
It seems to me that you’re not really attacking Plantinga here as much as you are attacking modal logic.
>what you seem to be arguing is “hey look, if you take modal logic seriously, you could prove anything in mathematics this way, but that’s absurd.”
Well, no. No absurdities result from merely “taking modal logic seriously.” To get to the point where you can prove anything with modal logic, you have to do a combination of two things: (1) accept S5 and (2) think you can just assume things are possible.
I’m okay with (1) and think the problem is with (2). You could also avoid the absurdities by rejecting S5. Either way, it undermines Plantinga’s argument.
Deus Ex Machina: “It seems to me that you’re not really attacking Plantinga here as much as you are attacking modal logic.”
No. As both Chris and Plantinga point out, the premise in question is the claim that god (as a necessary being) is possible.
The theist will accept this premise because she thinks that god is actual, but the atheist should reject it (since if a putatively necessary being is non-actual, then it is impossible).
The debate between Chris and Plantinga is over the question of whether the argument shows that it is “reasonable” to believe in god. On this point I side with Chris, but it’s not easy to specify what makes beliefs reasonable or not.
Deus Ex Machina- You’ve misunderstood his point.
There are two types of possibility. Lets call one “actual” possibility, and the other “epistemic” possibility. Actual possibility reflects the idea that things “could” be a particular way. Epistemic possibility reflects the idea that “for all I know, things could” be a particular way.
Its possible for something to be epistemically possible, but not actually possible.
For example, the solution to a really complex math problem might, epistemically, be “4.” That is, for all I know, the answer may be 4. But it may not be ACTUALLY possible for the answer to be 4. Because if the answer is ACTUALLY 8, then that’s the only thing the answer could be.
You could contrast this with, say, a problem about the contents of a box. Suppose that tomorrow I am going to put an object in a box, and you have to guess what it is. Epistemically, you might say that its possible that the box will hold a book. That is, for all you know, it may hold a book. And that may also be an ACTUAL possibility, in that it is actually possible that you may be right.
In the math problem, it can be proven that there was literally no possibility whatsoever that 4 was the right answer. All you have to do is solve the problem. But with the box, even if it turns out that it contains a book, there was a possibility that it wouldn’t.
This is all well known to people who do modal logic.
“and (2) think you can just assume things are possible. … [I] think the problem is with (2).”
That might work if Plantinga were “just assuming” by assertion that the existence of God is possible. But this argument, as far as it goes, doesn’t even address that. The discussion at this point, rightly, ought indeed move to whether the existence of God is or is not possible. But the argument here merely tries to show that if you do indeed accept the possibility of God’s existence, then God’s actual existence follows. According to this last comment, now, you aren’t even denying that (though it’s odd that you now say you’re okay with S5 despite seeming to attack it in the post). If so, you aren’t even objecting to the argument at any level at all – you’re accepting it and then giving your own personal opinion on the first premise (which seems to just be that you don’t know whether the existence of God is logically possible or not). It seems to me that that amounts to moving forward with the argument, and not rejecting it; and that would seem to imply that you really don’t, after all, think Plantinga’s argument “isn’t even halfway good.”
On a separate topic… Plantinga’s ontological argument reminds me of Matt Slick and his presuppositionalism. At least… the way the ontological argument is popularly used reminds me of it. I’m not sure Plantinga himself would use it in this manner.
Slick has this entire sales pitch he does for theism where the key is to get you to agree to certain premises before you fully understand what he means by them. Then he attempts to beat you over the head with arguments based on these premises. In essence, he gets you to agree to certain statements about what justifies believing something, and then attempts to beat you up with the regress problem of epistemology. Simultaneously, he gives himself an all clear on the regress problem by declaring that God solves it by magic.
The modal ontological argument does a similar thing in its popular usage. The key is to get the non believer to agree with the statement “it is possible that God exists.” Then you swap out the meaning the atheist thought they were using (for all I know, it is at least possible that God could exist) for a new meaning they didn’t anticipate (there exists a possible world in which a being exists who exists in all possible worlds), and beat them up with it.
Again… I’m not sure that Plantinga really meant to create a shady apologetic bait and switch. But he did.
This is the point, in the nature of necessity Plantinga argues at length for the possibility of God’s existence. I mean, I don’t understand how you can claim that these people “just assume these things without argument”.
I mean, Plantinga certainly doesn’t just “think you can just assume things are possible”. He certainly thinks God’s existence is epistemically possible, and he goes on to give arguments why it is actually possible.
Like I mentioned to Chris on Facebook, this blog isn’t much of an argument at all. The way to attack Plantinga is not to paint him as “merely asserting things are actually possible” since that’s clearly a strawman, rather you ought to engage with the question of whether or not God is *actually* possible. Unless you think that’s a question impossible to answer (which would put you in a position that not many atheists share since there’s plenty of literature out there that tackles the coherence of God’s attributes) then that’s the route you ought to take. Regardless, people like Plantinga don’t just “assume” this stuff out of their ass (that’s a nice little atheistic narrative that anyone familiar with the literature would laugh at). He argues *for* it; not just Plantinga, but folks like Swinburne in “The coherence of Theism” do so as well.
There are problems with the Modal Ontological argument, this blog doesn’t show what they are though.
“Then you swap out the meaning the atheist thought they were using (for all I know, it is at least possible that God could exist) for a new meaning they didn’t anticipate (there exists a possible world in which a being exists who exists in all possible worlds), and beat them up with it.”
Do you then claim that *all* atheists are (or should be) convinced by incoherence arguments for the existence of God?
No. I claim that in casual conversation, when a non believer says that its “possible” that god exists, he typically means “for all I know.” He doesn’t mean “there exists a possible world in which a being exists that also exists in all possible worlds.”
Interestingly, you claim that Plantinga argues for the possibility of God’s existence, presumably in terms of s5 modal possibility rather than epistemic possibility. I find it odd that you would say that seeing that you didn’t know the difference at 12:27 PM today, but possibly you have educated yourself in the interim. What, precisely, are Plantinga’s arguments for the modal possibility of a modally necessary being? I was under the impression that he hadn’t any.
Bear in mind, of course, that proving the possible existence of a necessary being requires proving the actual existence of that necessary being. In fact, it requires quite a lot more than that, because to prove that said being was necessary you’d have to prove that it was logically impossible for that being not to exist, not merely that the being does in fact exist. But proving its actual existence would be a start.
@Ashtad: You write:
>But the argument here merely tries to show that if you do indeed accept the possibility of God’s existence, then God’s actual existence follows.
That appears to be contradicted by Plantinga’s own words, which you yourself quote on Facebook: “What I claim for this argument, therefore, is that it establishes, not the truth of theism, but its rational acceptability.”
So Plantinga claims to have demonstrated the rational acceptability of theism, and not merely the conditional claim you cite in your comment here.
@Deus Ex: in case you’d rather continue the discussion here instead of on Facebook, I’m copying part of a comment from there to here:
“Is it obviously reasonable to believe that it is broadly logically possible that the Goldbach conjecture is true? And if not, what’s the difference?”
I wouldn’t mind hearing Ashtad answer those questions either.
>>But the argument here merely tries to show that if you do indeed accept the possibility of God’s existence, then God’s actual existence follows.
>That appears to be contradicted by Plantinga’s own words, which you yourself quote on Facebook: “What I claim for this argument, therefore, is that it establishes, not the truth of theism, but its rational acceptability.”
Right. We seem to be in worse shape than I thought, if you don’t already see that these are not mutually conflicting claims.
Why does Plantinga think the argument establishes the rational acceptability of theism? Because he thinks the premise is rationally acceptable, and he thinks the modal logic of the argument he put forward is sound. He doesn’t claim to have proven the first premise within the text of ‘The Ontological Argument’ itself; and indeed, that is exactly why he explicitly admits that the argument does not “establishe … the truth of theism….” You seem to have taken “rational acceptability” to mean something Plantinga himself didn’t intend, and misconstrued his aims on that basis.
Quoting from paragraphs 55 and 57, “What shall we say of this argument? It is certainly valid; given its premise, the conclusion follows. The only question of interest, it seems to me, is whether its main premise — that maximal greatness is possibly instantiated — is true. I think it is true; hence I think this version of the ontological argument is sound. … but 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.” And it’s at this point that he makes his concluding statement (quoted above).
So Plantinga himself clearly thinks the first premise is true. But the text of ‘The Ontological Argument’ just simply doesn’t address whether we should or should not accept it one way or another; that’s beyond the scope of that paper, and a different discussion altogether. This is presumably a discussion Plantinga would be well capable of joining and defending himself in (as Andres notes). So to say that the argument fails because Plantinga doesn’t conclusively prove the first premise—when Plantinga fully admits as much himself; states explicitly that it is beyond the purpose of ‘The Ontological Argument;’ and leaves it to be addressed elsewhere—is just totally misplaced.
In any case, what he means in claiming that the argument establishes the “rational acceptability” of theism is that, since the logic is valid, and the premise is (at least) not unreasonable, accepting the conclusion is therefore not unreasonable either. If you aren’t denying its validity (and by your apparent admission in the comment I replied to above, you aren’t), then you’re admitting that it is, at least, “halfway good” (as is all Plantinga claims within that text) and you aren’t criticizing anything in the actual text of ‘The Ontological Argument’ at all.
“Interestingly, you claim that Plantinga argues for the possibility of God’s existence, presumably in terms of s5 modal possibility rather than epistemic possibility. I find it odd that you would say that seeing that you didn’t know the difference at 12:27 PM today, ”
Actually, I’ve known the distinction all along. *You* folks claimed I misunderstood Chris’s objection because of my lack of knowledge about the distinction, which is not the case whatsoever since my objection still stands. Chris’s objection does not work because he relies on the claim that Plantinga merely “asserts” the actual possibility of God and lets the argument work from there. That’s not true, I mentioned a good place to start would be the nature of necessity, and even if Plantinga himself does not argue for it, it’s perfectly okay for him to rely on the work of others who do so like Swinburne.
I don’t remember all the steps right now, it’s been ages since I’ve read the relevant stuff so any explanation here would be half assed, and it doesn’t matter if I can’t explain all of Plantinga’s arguments because all I’ve stated is the fact that he *does* indeed argue for the actual possibility of God’s existence. Whether his arguments are successful or not is irrelevant here, the simple point I’m making is this “Plantinga is fully aware that for this argument to be rationally compelling to a non-believer, you must give an argument in favor of the first premise.” If you think I’m wrong about this, I’d like you to cite textual evidence that shows Plantinga is unaware of this.
I’m not going to get sidetracked into getting into Plantinga’s arguments for actual possibility nor will I defend them here, I’m not a Christian, and once again, it is all irrelevant. The question is, *does* he provide arguments for it at all? Yes. If you disagree, well, feel free to check out the book yourself.
Chris, in your time as a philosophy student at Notre Dame, did you met and/or talk with Plantinga?
@Ashtad,
>Right. We seem to be in worse shape than I thought, if you don’t already see that these are not mutually conflicting claims.
Well, I’ll agree that we are in worse shape than I thought. Would it help if I emphasized that I object to the “merely” in your statement?
@Annatar: I ended up in the same room with him once or twice, but never talked to him much. He retired after my first semester. In that first semester, I passed on an opportunity to take a seminar with him–the seminar was titled “Christian Theism & Problems of Philosophy,” and I sort of got the impression it was aimed at believing Christians.
I bet you could have made a name for yourself as an obnoxious prick in that class though
More @Ashtad:
I take it that if you are trying to do X, and also trying to do Y, you are not merely trying to do X, correct?
So if Plantinga was trying to show that if you do indeed accept the possibility of God’s existence, then God’s actual existence follows, and also trying to establish the rational acceptability of theism, then he was not merely trying to do the one, correct?
Plantinga is very famous for his demonstration that there is *one* possible world in which his god and evil can co-exist.
In other words, Plantinga’s claim that his god exists in *all* possible worlds is countered by his desperate attempt to find *one* logically possible world in which his god exists and his blatant admission that there are is a vast number of logically possible worlds where his god could not exist.
So how can one Plantinga claim his god exists in all logically possible worlds, while the other Plantinga has to scour around the realms of fantasy to find even one logically possible world to try to defeat the problem of evil?
‘ it’s perfectly okay for him to rely on the work of others who do so like Swinburne.’
Is that the Swinburne who maintains that his god is not a logically necessary god, or a different Swinburne?
ASHTAD
So to say that the argument fails because Plantinga doesn’t conclusively prove the first premise—when Plantinga fully admits as much himself; states explicitly that it is beyond the purpose of ‘The Ontological Argument;’ and leaves it to be addressed elsewhere—
CARR
More pass-the-parcel apologetics.
This argument fails, but if you look in another book, you will see it is addressed there….
And when you open that parcel, you find it is also empty!
Hi Chris
I’ve always taken Plantinga’s claim about the work his MOA does to be that it shows that belief in god is reasonable *if the belief that god’s existence is possible is reasonable*. But if this is the case, then I’m not sure if your criticism (as currently formulated) has any purchase.
Now you might say that if this is what Plantinga is up to, then his conclusion is trivial, since it shows that any claim that involves a necessary truth is reasonable if the notion that it’s possible is reasonable. But I think that whether it’s trivial depends heavily on the context of the current debate, so if it’s the case that both (1) it’s controversial that X is reasonable, and (2) most people would concede that X is possible (or, minimally, that it’s more likely true that X is possible than it is that X is impossible), then such an argument might contribute something useful to the debate.
Eric- the objection is, in part, that saying that a purported necessary truth is actually necessarily true if its possibly true isn’t actually that insightful. And in fact, if you want to prove that its possible that a purported necessary truth is true, you have to prove that its actually true.
Otherwise what you end up with is a claim that its epistemically possible that a purported necessary truth is possibly true. Which isn’t any more useful than saying that its epistemically possible that a purported necessary truth is actually true. Which is the thing you wanted to prove.
Modal logic is a mouthful.