Ok I understand that, but if God's existence is even POSSIBLE, then God must exist. When dealing with the nature of necessity, all that is required is the minimum possibility. Once that is established, then it logically follows that what is possibly necessarily true is in fact necessarily true.
Sorry idav, but that won't work given the fact that the Modal Ontological argument is logically sound.
1. It is at least possible for a MGB (maximally great being) to exist.
2. If it is possible for a MGB to exist, a MGB must exist in some possible world.
3. If a MGB exists in some possible world, a MGB must exist in all possible worlds.
4. If a MGB exists in all possible worlds, a MGB must exist in this world.
5. Conclusion: A maximally great being exists in this world.
Now 2-5 just follows logically from 1. The only way out of this is for you to negate the first premise, which I don't think you can do. So as long as #1 is true, 2-5 just follows logically.
So as long as it is possible for God to exist, there can't be an "if God doesn't exist" scenario at which such a proposition can possibly be true. That is like saying "If a one-sided stick does exist..." the statement alone is incoherent and while you can certainly make the statement, there can be no truth value to the statement.
Here is my updated objection to Plantinga's Ontological Arument, which I believe overides any formal proof.
Plantingas argument follows the form of logic known as Axiom S5 that states if a thing's definition only allows it to exist necessarily, which of course it does in this case, then if there is a possible world in which it exists, it exists in all possible worlds. Now every world that isnt necessary is contingent, and therefore possible worlds are possible beings. By definition the concept of Supreme Being is the only necessary being, and thus there are no possibly necessary worlds. And if God can be conceived to be non-existent in this the actual (and therefore) possible world then it follows that there is no Maximally Great Being in every world, which means that no Maximally Great Being exists of necessity. Now from this point I must mention John Locke, who said there is no innate idea of God, which would seem to be correct. Even theist philosopher Descartes showed with his Cogito ergo sum that he was unable to conceive of himself as being always in existence; he said "I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind." And that is to say when he is not thinking then by his own argument there can be nothing always necessarily in existence, not himself and not God. Thus his first principle (and his proof of God) failed.) And as Hume said it will always be possible for us at any time to conceive the non-existence of what we formally conceived to exist. He also said: nor can the mind lie under a necessity of supposing any object to remain in always in being in the same manner that we lie under the necessity of always conceiving twice two to be four.
In sum, there is no entailment from God has necessary existence to Necessarily God exists. For if it is possible to conceive the non-existence of any object then its non-existence is possible and therefore it cannot be necessary. There is no being or entity that imposes its necessary existence on my thoughts; there is therefore no necessarily existent entity. The three Aristotelian laws of thought, which are intuitive and demonstrable, are the law of non-contradiction, the law of excluded middle, and the law of identity, all of which in simple terms mean that we cannot think what cannot be thought. Consider the principle of identity, A=A is analytic: (a thing is the same as itself). Notice it isnt possibly necessary but immediately, intuitively, and necessarily certain. If Almighty God, the creator of all things is a Maximally Great, necessarily existent being it would be as absurd to deny that truth as it would be say A=A is false - and with equal veracity. If a thing is necessary and an absolute truth then it cannot be thought as false as with the 2 + 2 = 4 example that Hume mentioned. Similarly a thing that is all red cannot at the same time be conceived of as being all blue; its an impossible conception, as would be an object that is not the same as itself. And yet, regardless of any definition, concept, or proposition we can conceive of there being no God, which would be impossible if Gods existence is necessary, certain and true. The real existence of an object cannot be demonstrated via a proposition (which of course is why nobody believes in God because of the ontological argument); at most all that can be done is to show that the conclusion follows from valid premises and in which case the conclusion is said to be sound. So the soundness is arrived at due to the validity of the premises and not to any factual or ontological certitude; therefore one cant suppose the existence of a necessarily existent being by virtue of the terms and their relationship in a sentence. But in any case what actually governs logical expressions is the question of whether we can think what cannot be thought. And whatever can be conceived of as existent can also be conceived to be non-existent, and since the God concept can only exist in the mind when its thought of, there is therefore no God that can be thought as remaining always in existence. And on that account it self-evidently cannot be necessary.