The Anti-Ontological Argument
The ontological argument proceeds from the premise that God contains all perfections to the conclusion that God exists. The anti-ontological argument proceeds from the premise that God contains all perfections to the conclusion that God does not exist. It thus precisely reverses the traditional argument deriving from Anselm.  Anselm argued that God could not be merely imaginary, because his definition as the most perfect conceivable being logically implies his existence, existence counting as a type of perfection. The anti-ontological argument contends that God must be merely imaginary, because his definition as the most perfect conceivable being logically implies his non-existence, since no absolutely perfect being can possibly exist (though such a being can certainly be imagined). This argument, like its traditional counterpart, operates with a very simple principle, which may be stated thus: For any kind K, nothing that exists could ever fall under the concept perfect K. Consider, for example, the kind hammer and form the concept perfect hammer: you have now gone from a concept with existent instances to a concept with no existent instances. Why? Because there can be no such thing as a perfect hammer, since every existent hammer will be imperfect in one respect or another. Only imaginary hammers are perfect; real hammers always have flaws and drawbacks and weaknesses. Every hammer will fail to hit the nail on the head once in a while; every hammer will occasionally hit your finger instead; every hammer costs money to buy; every hammer gets rusty and decays; every hammer weighs something; every hammer takes several knocks to drive the nail home. There is no point in going into a hardware store and asking for the perfect hammer; there is no such thing. There are only more or less imperfect hammers. True, you can conceive of a perfect hammer stipulated to have none of the defects listed, but there can’t be such a hammer. That’s not how the world works: there are always downsides and side effects and boundary conditions. It is the same for knives, motorcars, houses, musical instruments, and other artifacts. Ditto for organs of the body, and indeed whole organisms. Nor are persons any different: there is no perfect teacher or perfect policeman or perfect violinist. Everything is flawed in one way or another. Everything fails to live up to our imaginary ideals. Only non-existent objects lack any imperfection, because they are so stipulated. The real world always carries attributes that exceed and diverge from the ideal function of a type of object; thus no object functions ideally, as a matter of principle. Nothing is functionally perfect.
But God is defined as all perfect, absolutely perfect in every respect, without flaw or failing of any kind. The ancient Greek gods were not so defined, so there is no logical or metaphysical obstacle to their existence: but the god of monotheistic Christianity (and other religions) is decreed to be entirely without imperfection. Certainly we can imagine such a being, given the powers of the human imagination; but by our principle this being could not exist in the real world. The more we stipulate God’s supreme perfection the more we remove him from the realm of reality. In the real world God’s great powers and virtues would come with accompanying drawbacks, such as unintended side effects or large expenditures of energy or the exclusion of alternative desirable states of affairs. But we are told that none of this is true of God: when God acts there are no unfortunate correlates, no cons to the pros. His being and his actions are perfection through and through. He doesn’t even take up space thereby preventing other good things from existing! But this is simply defining him out of existence, like allowing that no actual terrestrial hammers are perfect while insisting that there are perfect hammers somewhere else in the universe (“transcendental hammers”). If someone were seriously to claim that, you would naturally ask what kind of hammer this could be: what material is it made from, how does it escape the laws of nature, how does it operate? In the case of God we are schooled not to ask these kinds of question, but the price is that we are merely confusing the imaginary with the real. The concept perfect being has no existent extension, where being is taken to mean some sort of person-like entity. Thus that concept logically implies the non-existence of whatever falls under it (i.e. imaginary objects). If we take the concept of perfection to imply something functional, such as performing the office of a god perfectly, then no existent entity could ever be functionally perfect in the sense intended. In fact, when God is conceived as imperfect, as he sometimes is in the Old Testament, we have a clearer idea of what an existent entity of this kind might be like; but once we stipulate that there is nothing imperfect about him we enter the realm of the unreal and merely imaginary. Just as there are no perfect circles in the real world, only ideally, so there are no perfect gods in the real world, only ideally. The only circles that exist are imperfect.
Here it might be objected that perfect circles can exist in Plato’s heaven—the same kind of place in which God is supposed to exist. But this is a confused thought, because such ideal entities do not act in the real world: they may be claimed to have genuine existence (as opposed to be being merely imaginary idealizations) but they don’t do anything to change the course of events. God does: he is supposed to be an active agent, a powerful force, a driver of change. That is, he is supposed to be as other active agents are—a type of (very superior) person, not an inert abstract form. God isn’t a piece of abstract geometry eternally at rest; he is capable of intervening in history. But then he must have whatever imperfections come with the territory: he can’t be both of the world and yet not of it. If he has a will, he has to have whatever imperfections come with that—anything else is merely imaginative stipulation. To deny this is like saying that a perfect knife has an ideal cutting edge without recognizing that no existent knife can have a cutting edge free from all imperfection. We can say the words but no real knife could live up to them (it would have to be unable to cut the flesh of its user for one thing). Why should a god be any different?
You might say that an existent God could have all moral perfections. That is not as easy as it sounds, but anyway it won’t preserve the traditional Anselmian notion of God, since it is compatible with accepting multiple imperfections of other kinds. That is, there might be a morally perfect being with bad teeth, a limp, a weakness for chocolate, poor taste in music, and a horrible dress sense. Such a being could exist without violating our principle, but he doesn’t add up to God. It is the requirement that God be perfect in every way and in every particular—absolutely and totally perfect—that puts him beyond the realm of actual existence. We just can’t comprehend what this would be—just as we can’t comprehend an actual perfect circle (one drawn with the intention to approximate the platonic ideal). If we define God in this way, we define him out of existence: we place conditions on his existence that can’t be realistically met. Suppose we say (with Spinoza) that God is composed of an infinite immaterial substance: that substance will exclude other substances like it, thus precluding a second all-perfect God from existing (itself a drawback); but it also raises the question of how such a substance might operate and what prevents it from malfunctioning. How could any substance exist and yet be incapable of failing to function as intended? How could it not at least contain the seeds of imperfection? To think otherwise is to lapse into a fairytale land subject only to the laws of imagination. It is to deal in metaphysical nonsense. We can appreciate this point easily for hammers, knives, and policemen, but in the case of God piety prevents us from applying our principle consistently. We tacitly concede this when we ignore the question of God’s aesthetic properties: is God perfectly beautiful too? No existent thing is ever perfectly beautiful—the very idea is a fantasy—so how can God be perfectly beautiful? What does that even mean? Is he superlatively handsome? Does he have a lovely form than which no lovelier form can be conceived? Is his beard finer than the finest silk? None of this makes sense—so how does God possess all aesthetic perfections? The anti-ontological argument contends that any actual being with aesthetic qualities will have aesthetic imperfections or limitations; aesthetic perfection obtains only in the realm of the ideal or imaginary. The right thing to say is that we can conceive of an all-perfect being (or at least we can say those words) but that no such thing could exist in reality. Thus the definition of God as an all-perfect being logically implies that God is not real—just like the definition of an all-perfect knife (call it “Excalibur”) implies its unreality. If we knew there to exist gods that are less than perfect, we would accept no counter-example to our principle; suggesting that there is a different type of god that is perfect in every way would naturally arouse our suspicions, for it would violate our general conception of reality. We know that reality is less than ideal, and we know that we can conceive of things that are ideal; so we naturally reject the idea of the ideally real. We find the conjunction of the attributes of complete perfection and real existence to be contrary to reason.  The concept of absolute perfection is hyperbolic and fails to characterize the real world. It is this concept that is deployed in defining God as Anselm does in the ontological argument: but that definition asks too much of any actually existent entity. Thus the Anselmian definition of God, so far from entailing God’s existence, logically precludes it.
 In what follows I don’t attempt to say where Anselm’s argument goes wrong; instead I offer another argument with the opposite conclusion. If this argument is sound, we know that Anselm’s argument has to go wrong somewhere. For the record, I think he is wrong to take existence as a type of perfection.
 I hope no one will protest that perfect numbers exist (a positive integer that is equal to the sum of its proper positive divisors): that is not the notion of perfection at issue. And of course there is no objection to the loose use of “perfect” in conversational contexts.