Since God’s necessary existence is on the one hand admitted to be an existentially neutral truth about the idea of God, and moving from this existentially neutral truth about God to an existential claim about God is what is principally attacked when ontological arguments are offered, why not give a Kantian style argument for God’s existence as necessary for philosophical consistency? In other words, Kant argued in the critique of the power of judgment that it is irrational and intellectually unconscionable to fail to postulate ‘God’ for the sake of a coherent philosophical system (the reflective power of judgment). In particular he wants us to postulate God in order to make sense of biological organisms and the whole notion of physical teleology supposedly bound inexorably up therewith. My argument here won’t tread in that direction. I’m just trying to make Descartes’ essential point that to say “God doesn’t exist” is quite like saying “I have an idea of a triangle, and it’s just like your idea of a triangle with the exception that my idea is one of a shape which has four sides” – the person who says this reveals to the rest of us that they just haven’t understood the idea yet, and they do not, therefore, have the same idea in mind.
So, since the argument against ontological arguments is that one can’t legitimately get from “the idea of X involves its existence” to “the idea of X entails its existence,” why not construct a more modest epistemic argument which goes from “the idea of X involves its existence” to “the statement ‘X does not exist’ is confused and unintelligible, and thus does not express a logically possible scenario”? That pushes the debate back to something like between Theism and non-cognitivism concerning Theism. The only way to rationally avoid believing that X exists is to argue that there is no coherent idea of X (either because X involves contradictory attributes, or because everything we say about X amounts to or reduces to saying nothing at all). Thus, only the person who thinks either that Atheism is an analytic a priori truth, or a positivist, can rationally avoid Theism; any weaker form of Atheism or Agnosticism, is in trouble.
Now, I think that the person who is willing to claim that some apparently meaningful statement is meaningless has, in so suggesting, accepted a burden of proof – it is up to them to demonstrate vacuity, not up to us to demonstrate meaningfulness. As a rule of thumb, one should always prefer to enrich modality rather than impoverish it, and so some statement should be considered prima facie possible (and thus meaningful) even if it isn’t clear how the world would look if it were true. However, positivists (or Logical Empiricists, who are really just Positivists in a brand new tuxedo), can’t cash this out; there just is no way to accept that burden of proof and advance the claim that “God exists” is meaningless.
On the other hand, what argument could be advanced to show that the idea of God involves logical contradiction? No successful argument has ever been presented, or at least no argument has convinced any significant number of philosophers. However, unless the Atheist can make the non-cognitivist move, or else make this rationalistic move, they, it seems, can’t sustain their Atheism coherently. If there is some X the very idea of which involves its existence, then there just is no way to argue that the sentence “X does not exist” is meaningful. So, perhaps instead of pushing a full ontological argument, we can first demonstrate that one cannot ever meaningfully think, speak or say “God does not exist” without either equivocation or confusion. If the Atheist says that their idea of God is of a thing which does not involve it’s existence, then they are equivocating – they haven’t got in mind what the Theist has in mind. However, for anything, if its idea involves its existence, then it cannot be thought to not-exist, even if one could rationally fail to think that it does exist (by arguing that there is no such coherent idea) one could not rationally think it to not exist. That makes it the case that all one needs in order to be rationally compelled to admit the existence of God is the idea of God. For an Atheist in whose mind exists the idea of God to claim that “just because it is not logically possible that “God does not exist” doesn’t mean one should conclude that God exists mind independently” is just for that Atheist to reject rationalism. Perhaps the Atheist will be alright with incurring that cost (after all, most Atheists are empiricists instead of rationalists anyways) but at least she should be aware of the intellectual attraction of Theism.
What is more, that Atheist (the one who admits to having a coherent idea of God which involves God’s existence) will have to be a ‘nominalist/relativist’ (not entirely sure what to call it) about modal properties. They will admit that the sentence “God exists” is de dicto necessary, and deny that God is de re necessary. They will say that God exists in all logically possible worlds (or at least that there is no logically possible world in which God doesn’t exist – not sure that leaves any room for a distinction) but deny that God actually exists. The sentence “God exists” is as de dicto necessary as the sentence “a unicorn is an animal, or, a bachelor is an unmarried man. Moreover, this doesn’t just define God into existence in some ad hoc way, since existence is not ‘added-on’ to the idea of God, but belongs to the complete concept of God. This epistemic-ontological argument can lower the ‘apologetic bar’ so as to possibly impress even transcendental idealists. It also makes it clear that one shouldn’t be allowed to get away with saying that they understand Theism as a coherent proposal and that they are within their rational rights to reject it. They must opt either for the position that Atheism is an analytic truth, or else for the position that the sentence “God exists” or the negation thereof, is just entirely vacuous – and both of those come with burdens of proof that, I think, can’t be met, and more to the point neither allows for the sentence “God exists” to be meaningful.