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 my 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” – we’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 we’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.