Alvin Plantinga famously defends a version of the ontological argument that makes use of the notion of possible worlds. As is typically done, we might think of a “possible world” as a complete way that things might have been. In the actual world I am writing up this blog post, but I could have decided instead to go pour myself a Scotch. (Since it’s still morning, I won’t—I can wait an hour.) So, we might say that there is a possible world more or less like the actual world—Obama is still president, I still teach and write philosophy, and so forth—except that instead of writing up this blog post at this particular moment, I am pouring myself a Scotch. (Naturally there will be some other differences that follow from this one.) We can imagine possible worlds that are even more different or less different in various ways—a possible world where the Allies lost World War II, a possible world in which human beings never existed, a possible world exactly like the actual one except that the book next to me sits a millimeter farther to the right than it actually does, and so forth. Not everything is a possible world, though. There is no possible world where 2 + 2 = 5 or in which squares are round.

Philosophers make use of the notion of possible worlds in all sorts of ways. For example, it is sometimes suggested that we can analyze the essence of a thing in terms of possible worlds: What is essential to X is what X has in every possible world, what is non-essential is what X has in some worlds but not others. It sometimes suggested that modality in general can be analyzed in terms of possible worlds: A necessary truth is one that is true in every possible world, a possible truth one that is true in at least one possible world, a contingent truth one that is true in some worlds but not others, an impossible proposition one that is true in no possible world. Plantinga, again, makes use of the notion in order to reformulate the ontological argument famously invented by Anselm. We might summarize his version (presented in The Nature of Necessity and elsewhere) as follows:

1. There is a possible world W in which there exists a being with maximal greatness.
 
2. Maximal greatness entails having maximal excellence in every possible world.>
 
3. Maximal excellence entails omniscience, omnipotence, and moral perfection in every possible world.
 
4. So in W there exists a being which is omniscient, omnipotent, and morally perfect in every possible world.
 
5. So in W the proposition “There is no omniscient, omnipotent, and morally perfect being” is impossible.
 
6. But what is impossible in one possible world is impossible in every possible world.
 
7. So the proposition “There is no omniscient, omnipotent, and morally perfect being” is impossible in the actual world.
 
8. So there is in the actual world an omniscient, omnipotent, and morally perfect being.

Plantinga famously concedes that a rational person need not accept this argument, and claims only that a rational person could accept it. The reason is that while he thinks a rational person could accept its first and key premise, another rational person could doubt it. One reason it might be doubted, Plantinga tells us, is that a rational person could believe that there is a possible world in which the property of “no-maximality”—that is, the property of being such that there is no maximally great being—is exemplified. And if this is possible, then the first and key premise of Plantinga’s argument is false. In short, Plantinga allows that while a reasonable person could accept his ontological argument, another reasonable person could accept instead the following rival argument:

1. No-maximality is possibly exemplified.
 
2. If no-maximality is possibly exemplified, then maximal greatness is impossible.
 
3. So maximal greatness is impossible.

In The Miracle of Theism, atheist J. L. Mackie argues that even this concession of Plantinga’s overstates the value of his ontological argument. For it is not at all clear, Mackie says, that a rational person can treat the question of whether to accept either Plantinga’s argument or its “no-maximality” rival as a toss-up, as if we would be within our epistemic rights to choose whichever one strikes our fancy. Why wouldn’t suspense of judgment in the face of such a deadlock, a refusal to endorse either argument, be the more rational option? Indeed, if anything it is the “no-maximality” argument that would be the more rational choice, Mackie suggests, in light of Ockham’s razor.

But though I do not myself endorse Plantinga’s argument, I think these objections from Mackie have no force, and that even Plantinga sells himself short. For it is simply implausible to suppose that, other things being equal, the key premises of Plantinga’s argument and its “no-maximality” rival are on an epistemic par. To see why, consider the following parallel claims:

U: There is a possible world containing unicorns.
 
NU: “No-unicornality,” the property of there being no unicorns in any possible world, is possibly exemplified.

Are U and NU on an epistemic par? Surely not. NU is really nothing more than a denial of U. But U is extremely plausible, at least if we accept the whole “possible worlds” way of talking about these things in the first place. It essentially amounts to the uncontroversial claim that there is no contradiction entailed by our concept of a unicorn. And the burden of proof is surely on someone who denies this to show that there is a contradiction. It would be no good for him to say “Well, even after carefully analyzing the concept of a unicorn I can’t point to any contradiction, but for all we know there might be one anyway, so NU is just as plausible a claim as U.” It is obviously not just as plausible, for a failed attempt to discover a contradiction in some concept itself provides at least some actual evidence to think the concept describes a real possibility, while to make the mere assertion that there might nevertheless be a contradiction is not to provide evidence of anything. The mere suggestion that NU might be true thus in no way stalemates the defender of U. All other things being equal, we should accept U and reject NU, until such time as the defender of NU gives us actual reason to believe it.

But the “no-maximality” premise of the rival to Plantinga’s ontological argument seems in no relevant way different from NU. It is really just the assertion that a maximally great being is not possible, and thus merely an assertion to the effect that Plantinga’s first and key premise is false. And while Plantinga’s concept of a maximally great being is obviously more complicated and harder to evaluate with confidence than the concept of a unicorn, it seems no less true in this case that merely to suggest that a maximally great being is not possible in no way puts us in any kind of deadlock. Unless someone has actually given evidence to think that Plantinga’s concept of a maximally great being entails a contradiction or is otherwise incoherent, the rational position (again, at least if we buy the whole “possible worlds” framework in the first place) would be to accept his key premise rather than the key premise of the “no-maximality” argument, and rather than suspending judgment.

(Mackie’s assumption that Ockham’s razor is relevant here—he speaks of not multiplying entities beyond necessity – also seems very odd to me. Appealing to Ockham’s razor is clearly in order when you are dealing with alternative explanations each of which is already known to be at least in principle possible, and are trying to weigh probabilities in light of empirical evidence. But questions about semantics, logical relationships, conceptual and metaphysical possibilities, and the like—the sorts of issues we are considering when trying to decide whether Plantinga’s key premise or its rival is correct—are not like that. The whole idea of applying Ockham’s razor to such issues seems to be a category mistake. But I won’t pursue the thought further here.)

Other objections to Plantinga are also oversold. There is, for example, the tired “parody objection” that critics have been trotting out against ontological arguments since Gaunilo, and which I suggested in a previous post have no force, at least against the most plausible versions of such arguments. For example, John Hick suggests (in his An Interpretation of Religion) that Plantinga’s reasoning could equally well be used to argue for the existence of a maximally evil being, one that is omnipotent, omniscient, and morally depraved in every possible world. The problem with this objection is that it assumes that good and evil are on a metaphysical par, and as I have had reason to note before, that is by no means an uncontroversial (or in my view correct) assumption.

But defending the idea that evil is a privation would require a defense of the more general, classical metaphysics on which it rests. And there lies the rub. For Plantinga is not a classical (i.e. Platonic, Aristotelian, or Scholastic) metaphysician. That is reflected not only in the way he conceives of God’s omnipotence, omniscience, and “moral perfection”—I’ve noted before that Plantinga is a “theistic personalist” rather than a classical theist—but also in the more general metaphysical apparatus he deploys in presenting his ontological argument. From a classical metaphysical point of view, and certainly from an Aristotelian-Thomistic (A-T) point of view, the “possible worlds” approach is simply misguided from the start (for reasons I’ve also had occasion to discuss before). Many no doubt think that Plantinga’s argument is at least an improvement on Anselm’s. I think it is quite the opposite. In no way do I intend that as a slight against Plantinga; on the contrary, The Nature of Necessity is, as no one familiar with it needs me to point out, a testament to his brilliance. But it is also, like the best of the work of the moderns in general, a brilliant mistake. A sound natural theology must be grounded in a sound metaphysics, which means a classical (and preferably A-T) metaphysics. Within the context of a classical metaphysics, Anselm developed as deep and plausible an ontological argument as anyone ever has. But (so we A-T types think) even he couldn’t pull it off.
 
 
NOTE: Dr. Feser's contributions at Strange Notions were originally posted on his blog, including this article, and therefore lose some of their context when reprinted here. Dr. Feser explains why that matters.
 
 
(Image credit: Live Science)

Over the coming weeks, instead of exclusively posting articles asserting and defending a particular view, we'd also like to feature open-ended discussion posts that lay on the table a popular argument for or against God and then invite us to discuss it together, as a community, in the comment boxes.

Today, we'll begin with Alvin Plantinga's modal ontological argument for God. Plantinga is one of the most respected and influential philosophers today. He's the John A. O'Brien Professor of Philosophy Emeritus at the University of Notre Dame and has written groundbreaking books on the problem of evil, God and science, and philosophical arguments for God.

His modal ontological argument for God relies on modal logic, which deals with the logic of possibility and necessity. Watch the nine-minute video below for a summary of the argument:

The video presents the argument like this:

Premise 1: It is possible that God exists.
Premise 2: If it is possible that God exists, then God exists in some possible worlds.
Premise 3: If God exists in some possible worlds, then God exists in all possible worlds.
Premise 4: If God exists in all possible worlds, then God exists in the actual world.
Premise 5: If God exists in the actual world, then God exists.
Conclusion: Therefore, God exists.

What's interesting about this argument is that it attempts to show that if God's existence is merely possible, then it would be necessary. Or to put it another way, the only way God couldn't exist is if his existence is impossible. Thus if Plantinga is right, any atheist who says "I don't believe God exists but it's at least possible" would, if he properly understands the argument and Plantinga's definition of God, be logically compelled to change his mind.

If the argument holds, it would also mean we can't say there's a 50%/50% chance of God existing, or that the odds are 10% or 90%. The only possibilities are 0% or 100%. Either God's existence is impossible (0%) or it's possible and therefore necessary (100%).

What do you think? Is the modal ontological argument for God a sound proof? If not, how does it fail?

There are a lot of good arguments against atheism (like the argument from contingency). There are also some good ones which unfortunately have been used incorrectly so many times that they have been misidentified as bad ones (like Pascal’s Wager). Even more unfortunately, there are also some genuinely bad ones (like the argument from the banana), and some of these are quite popular.

One of the worst is all the more dangerous because it sounds enough like a good argument that it is often made by seasoned apologists. I don’t think it has a name, but the idea is that in order for someone to know that there is no God, one would have to have to be God. Even the more “sophisticated” versions of this schoolyard argument are fallacious, and this needs to be called out before the argument does any more damage.

Proving Universal Negatives

It is popular in apologetic circles to argue that one cannot prove a “universal negative” (aka a “negative existential proposition”) such as “God does not exist.” This has some intuitive appeal – after all, how can one make an assertion concerning all of reality (i.e., “God does not exist anywhere.”) without knowing all of reality? Indeed, the famous atheist philosopher Bertrand Russell once admitted that when it comes to the existence of God, the proper “attitude may be that which a careful philosopher would have towards the gods of ancient Greece. If I were asked to prove that Zeus and Poseidon and Hera and the rest of the Olympians do not exist, I should be at a loss to find conclusive arguments.” However, the argument still fails as an apologetic strategy.

The underlying mistake is that the problem of proving a universal negative only applies to things that (at least) can possiblyexist. So, for example, it might be impossible to completely disprove the existence of unicorns, simply because of the difficulty of searching out every possible location such creature might inhabit (perhaps extending to other planets). Thus, it would be extraordinarily difficult to definitively prove that “there are no unicorns in existence anywhere.”

When it comes to the existence of Santa Claus, however, it would not be nearly as difficult. This is because the existence of a being answering to the standard description of Santa Claus can be shown to be definitively impossible. Rather than surveying all possible locations where such a being might be found, one can simply note that the conditions required for such a being to exist are essentially impossible.

Put another way, while I may not be able to prove the non-existence of any 10′ tall bachelors, I can certainly prove the non-existence of married bachelors. In a similar fashion, if one could show that based on the type of being that God would be if he existed that such a being was impossible, then the universal nonexistence of God could be known without “knowing it all.”

Requiring Godlike Powers

A corollary to the above mistake is the followup conclusion that one would need to be godlike oneself in order to coherently deny God’s existence. The idea is that one would have to be omniscient and / or omnipresent (know everything there is to know or be everywhere there is to be) in order to posses the knowledge that God does not exist, because anything less would leave the door open for God’s existence in a heretofore unknown part of reality. But omniscience and  omnipresence are attributes of deity. Thus the popular conclusion is that in order to disprove God, one would have to beGod.

This is a popular but philosophically ill-informed apologetic tactic. For example, seminary president and popular apologist Alex Mcfarland writes,

“It is important to realize something about being an atheist that even most atheists fail to acknowledge and that is that atheism requires omniscience (complete knowledge of everything).… An atheist is making a positive assertion that there is no God. The only way that anyone could make such an assertion would be to presume that he knew everything about everything.” (“The 10 Most Common Objections to Christianity”, 37-38).

The same claim is made by the president and founder of Christian Apologetics and Research Ministry (the top Evangelical apologetics website) Matt Slick:

"Then you cannot KNOW there is no God. . . . atheism is illogical. You cannot know there is no God. To do that, you’d have to know All things to know there is no God." (“An Atheist Says He Knows There Is No God”)

This argument is also made by Christian research institute president Hank Hanegraaff:

“Atheism involves a logical fallacy known as a universal negative. Simply stated, a person would have to be omniscient and omnipresent to be able to say ‘there is no God’ from his own pool of knowledge. Only someone capable of being in all places at the same time — with a perfect knowledge of all that is in the universe — can make such a statement based on the facts. In other words, a person would have to be God to say there is no God. Hence, the assertion is logically indefensible. By using arguments like this, you will often find that an atheist quickly converts to agnosticism and is thus making progress rapidly in the right direction.” (“The Folly of Denying God” CRJ, 1990)

The same conclusion is repeated by popular apologists Ron Rhodes and Kenneth R. Samples in their respective articles on dealing with atheists in the Christian Research Journal in the 1990’s.

The argument does not seem to be losing any steam, either. As late as 2013, Ravi Zacharias made a similar claim on his Facebook page:

These alleged requirements are really just another species of the previously-discussed problem of proving a universal negative. Only empirical inductive arguments that require as their support the totality of reality (a “perfect induction” on a universal scale) would fall into such a trap. Rational deductive arguments (especially those involving direct contradictions) do not suffer from this flaw. (Interestingly, given the generally poor reception of the only purely deductive argument for the existence of God – Anselm’s Ontological Argument – among theists and atheists alike, it may be the case that atheists actually have the upper hand in attempting to argue their position based on logic alone.)

Conclusion

This particular argument fails due to the basic difference between empirical-inductive and rational-deductive proofs for a universal conclusion. Because inductive arguments are (by definition) those which (usually) give only probable support to their conclusion, and are usually based on empirical facts for their support, the idea that one could use such a method to disprove God is clearly problematic. There are, however, purely rational deductive arguments which would (in theory) definitively prove their conclusion by demonstrating that the notion of God is self-contradictory. And, since these kinds of arguments are indeed given against the existence of God, then it is not the case that “atheism is logically indefensible” (at least on these grounds). Thus, it is also false that atheists would have to posses godlike powers to know that God does not exist, because contradictions can be proven with merely human abilities.

Although not a lot of atheists have spoken out against this specious argument, it is a very bad one and makes theists look bad. To my fellow theists, I ask that you please do not use this argument, and alert those who have to its failure.
 
 
(Image credit: Wikimedia)