A modal argument for God's existence - why it fails

Philosophers of religion out there - is there a version of a modal ontological argument which isn't vulnerable to the charge that the premise:

 1. It is possible God exists

just trades on the ambiguity between metaphysical and epistemic necessity/possibility? Maybe there is, but I have not spotted one yet given an admittedly brief survey.

Here is a simple modal argument for the existence of God:

1. It is possible God exists
2. If it is possible God exists, God exists at least one possible world
3. If God exists at one possible world he exists at all of them (being a necessary being)
4. Therefore God exists at every possible world
5. Therefore God exists at the actual world

Good argument?

Note first of all that if we have good grounds for supposing God does not exist at the actual world, then the logic of the above argument also requires that we have good grounds for supposing God does not exist at any possible world. That is to say, we have grounds for thinking it is impossible that God exists. And perhaps we do have such grounds - e.g. in the form of vast swathes of evil.

In response, theists may say: 'Ah but it is possible God exists, because I can imagine God existing - I can certainly imagine that the property of maximal greatness is instantiated, say.'



This is to muddle epistemic and metaphysical possibility. Epistemic possibility is what might be the case given our fallibility/ignorance. It's the for-all-we-know variety of possibility.

To illustrate: it is epistemically possible that 12 x 12 does not make 144. That's epistemically possible because I acknowledge my mathematical fallibility - I may have miscalculated. However, that epistemic possibility does not establish that it's metaphysically possible that 12 x 12 does not make 144. It isn't (given that mathematical truths are, while epistemically contingent, also metaphysically necessary). 12 x 12 = 144 at every possible world.

Similarly, that Hesperus is not Phosphorus is epistemically possible (I can imagine it turning out that there's been a major astronomical cock-up or conspiracy regarding the supposed identity of the evening and morning stars). However, as Kripke points out, given we are dealing with two rigid designators here ('Hesperus' and 'Phosphorus'), if Hesperus is Phosphorus, then at no possible world is it false that Hesperus is Phosphorus. So it is not metaphysically possible that Hesperus isn't Phosphorus, despite it being epistemically possible that Hesperus isn't Phosphorus.

In short, if there are good grounds for thinking that x is metaphysically impossible, pointing out that x is epistemically possible does not, in general, provide any sort of rebuttal. E.g. If there's good empirical evidence Hesperus is Phosphorus, then there is in turn good evidence that Hesperus is Phosphorus is true with respect to every possible world, notwithstanding the fact that it's epistemically possible that Hesperus isn't Phosphorus.

Now yes, God's existence is epistemically possible. I can imagine God existing.

But suppose God does not actually exist. Then his existence remains metaphysically impossible - God exists at no possible world.

So the epistemic possibility of God existing is entirely compatible with the metaphysical impossibility of God existing.

So suppose I have good evidence that God does not actually exist - evidence in the form of the evidential problem of evil, say. Then I have good grounds for thinking, not just that God does not exist at the actual world, but that it is metaphysically impossible that God exists - that God does not exist at any possible world.

It won't do to reply - 'Ah, but God's existence clearly is possible, as I can imagine God existing!' For that would be to invoke the wrong sort of possibility.

Indeed, Atheists might consider the above modal argument as a kind of logical amplifier for their conclusion that God does not actually exist. It allows them to move from: as a matter of fact God does not exist, to necessarily, God does not exist! So perhaps we should add it to our arsenal?

The other obvious problem (which I know others have raised) with this modal argument is that it similarly allows one to move from it's possible God does not exist to, God actually does not exist. And most theists acknowledge the possibility that God does not exist. Hence they are, by the same logic, required to move from that possibility - which they acknowledge - of God not existing to the conclusion that as a matter of fact God doesn't exist.

POSTSCRIPT.

What does Plantinga says is the aim of his argument. He says it is not a 'proof' of theism, but that it does 'establish' the rational acceptability of theism.

Does Plantinga's argument establish the rational acceptability of belief in God?

No. If Plantinga were right, it would then follow that if (as seems equally clear) it is not irrational to believe it's possible God doesn't exist, so we could similarly 'establish', by means of a mirror argument, the rational acceptability of believing that God does not exist.

But Plantinga thinks believing God does not exist is not rationally acceptable! That's the conclusion of his Evolutionary Argument Against Theism - he says the rejection of theism is self-defeating in a way that theism is not.

So, Plantinga, to be consistent, must consider the mirror premise that that it's possible God does not exist to be irrational, despite appearances to the contrary.

In short, the seeming rationality of both premise 1 and this premise may in each case quite easily be shown to illusory, depending on what case can be made for/against rational acceptability of theism.

But then Plantinga's modal argument for the rational acceptability of theism, and the above mirror argument for the rational acceptability of rejecting theism, clearly fail to, as Plantinga puts it, 'establish' the rational acceptability of either position.




Comments

Eric Sotnak said…
I have sometimes suggested that the shortest dialogue on the existence of God goes about like this:

Atheist: "I can conceive that God doesn't exist."
Theist: "no, you can't."
TheBillBomb said…
Given there is no consistent definition of God, these arguments fall down in contradiction far earlier. The sentence "it is possible that god exists" has no meaning in the sense "is it possible that 'god = Thor' and 'god = Ra' when 'Thor != Ra'"
Philip Rand said…
You see Dr Law

I can use your understanding of the world to demonstrate to you that the Plantinga modal argument does not fail (it may not be correct but it does not fail). I can construct his argument using your own use of meanings. I can achieve this by going beyond your own understanding in a way that you can recognise as appropriate developments of your own commitments.

For example, you do not develop your “Hesperus is not Phosphorus” analogy, i.e. “Hesperus is [always] not Phosphorous“ is not a fair sample rather the fair sample should be “nearly always Hesperus” and “nearly always Phosphorus” BUT “always a planet”.

So your committed position with regards to Hesperus and Phosphorus is not bullet proof, i.e. it does not give you what you want nor does it address the multiple generality of your committed attack.

However, if we concatenate the modal argument for the Jerne theory of antibodies (which we know is empirically true) with the Plantinga modal argument we can see that the Plantinga modal argument is indeed bullet proof.

JERNE ANTIBODY MODAL ARGUMENT:

1. It is possible an antibody internal-image exists.
2. If it is possible an antibody internal-image exists, an antibody internal-image exists at least in one possible configuration.
3. If an antibody internal-image exists in one possible configuration the antibody internal-image exists in all internal-image configurations (an antibody internal-image being necessary).
4. Therefore an antibody internal-image configuration exists in all possible antibody internal-image configurations.
5. Therefore an antibody internal-image exists in the actual world.

PLANTINGA MODAL ARGUMENT:

1. It is possible God exists
2. If it is possible God exists, God exists at least in one possible world.
3. If God exists in one possible world he exists in all of them (being a necessary being).
4. Therefore God exists in every possible world.
5. Therefore God exists in the actual world.

CONCATENATION OF THE MODAL ARGUMENTS:

By merging the two arguments we obtain a single logical bullet proof expression that handles multiple generality; containing both empistematic possibility and metaphysical possibility, dependent only on the chain of inferences and nothing intuitive.

F= antibody internal-image
G=God
R=world/configuration

∀x(Fx→∃ y[Gy& ∀z(Rxz↔z=y])& ∀y(Gy→∃x[Fx& ∀w(Rwy↔w=x)])

What is of note is that your attack on the Plantinga argument is in exactly the manner in which the Jerne antibody theory was also attacked by the scientific community.