Necessity is not evidence

[MindForgedManacle]

Although presented as a deductive argument, Plantinga's modal argument presupposes <God exists> and relies on that presupposition to "deduct" the conclusion.

I certainly don't fancy myself an expert, nor was I making a threat. Rather, I was making the point that in making the claim that Plantinga's argument is circular, you're actually implying all deductive arguments are circular, because Plantinga's argument is no more circular than they.

One general criticism of ontological arguments which have appeared hitherto is this: none of them is persuasive, i.e., none of them provides those who do not already accept the conclusion that God exists

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—and who are reasonable, reflective, well-informed, etc.—with either a pro tanto reason or an all-things-considered reason to accept that conclusion. Any reading of any ontological argument which has been produced so far which is sufficiently clearly stated to admit of evaluation yields a result which is invalid, or possesses a set of premises which it is clear in advance that no reasonable, reflective, well-informed, etc. non-theists will accept, or has a benign conclusion which has

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no religious significance, or else falls prey to more than one of the above failings.

I can only assume, as an expert, you're already aware of these failings; so it seems you're attempting to force acceptance of the premises and conclusion, when I've already stated the premises require the presupposition of to lead to the related conclusion, and as such do not reasonably follow.

All that Plantinga's argument presupposes is that a) modal realism is true and b) God's existence is not metaphysically impossible, and builds an argument from that. And given it's deductively valid, it does logically follow. But I agree it's certainly not persuasive; you do realize I'm an atheist, right?

Plainly enough, non-theists and necessitarian theists disagree about the layout of logical space, i.e., the space of possible worlds. The sample argument consists, in effect, of two premises: one which says that God exists in at least one possible world; and one which says that God exists in all possible worlds if God exists in any. It is perfectly obvious that no non-theist can accept this pair of premises. Of course, a non-theist can allow—if they wish—that there are possible worlds in which there are contingent Gods. However, it is quite clear that no rational, reflective, etc. non-theist will accept the pair of premises in the sample argument.

http://plato.stanford.edu/entries/ontolo...arguments/

Okay? I agree with that, nor does it contradict anything I've said on this matter. Given our "actual world" is but one of an infinite amount of possible worlds, it's clearly obvious atheists cannot accept that God exists in all possible worlds and still be rational.

This modal argument begins with several presupposed premises: other deductive arguments that do not begin with presupposed premises. Which is the objection I initially raised.

What? All arguments presuppose certain premises or positions. Plantinga's argument presupposes modal realism and that's just about it. The rest follows deductively if you accept modal realism and the definition of God as a Maximally Great Being.

And no, your original objection was "Maybe =/= Necessary". However, as I said, that's just misunderstanding Plantinga's argument. Under axiom S5 of modal logic, saying (as Plantinga's arg. does) something's "possibly necessary" is equivalent to saying "necessary".

Plantinga himself states:
[Plantinga Quote]

That's his opinion. The only thing holding up Plantinga's modal ontological argument is an agreement that the central premise is rational, I.e. by extension the argument is in effect:
Presupposing: <it is possible God Exists>
To conclude: Therefore <God Exists>
By Plantinga's own admission.

Or, more directly stated: If we presuppose: <God Exists>
We can reasonably conclude: <God Exists>

http://plato.stanford.edu/entries/ontolo...#PlaOntArg

Hah, no. Part of the reason Plantinga says the central premise (God's existence is possible, i.e he exists in at least one possible world) is because of supporting arguments such as Robert Maydoyle's Modal Perfection Argument, which is also a logically valid argument. What Plantinga's argument does, to use your format, is as follows:

<Modal Realism is true>
<God's existence is not impossible, which entails that he exists in some possible world under Modal realism>
<He's a Maximally Great Being, which - drawing from Maydoyle's MPA - includes necessary existence>
<Necessary existence is synonymous with existing in all possible worlds>
<Therefore God exists>

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The ontological argument is illogical, it is mere wordplay on completely baseless assumptions.

They're not illogical (some are logically valid), but as I'm an atheist, I certainly don't accept them. :p