asaris

There's a difference. Your example equivocates on the meaning of nothing. In formal logic, it would run:

~Ex, such x>God
H>{empty set}
Ergo, H>God

However, your following argument is somewhat more convincing:

That's not really important to the modal ontological argument, though it is a valid objection to the original, Anselmian version. (Descartes version involves other difficulties which are probably beyond the scope of this discussion.) What the objection amounts to is that Anselms proof doesn't prove quite what he wants it to prove. All that it proves is that, if God exists, he exists necessarily. But we have the following addition to Anselms argument:

1. If God possibly exists, he exists in some possible world (def. of possibility)
2. God possibly exists (premise)
3. Therefore, God exists in some possible world. (1,2)
4. If God exists, he exists necessarily (Anselm's argument)
5. Therefore, in the possible world in which God exists, he exists necessarily. (3,4)
6. If something exists necessarily, it exists in all possible worlds (definition of necessity)
7. Therefore, God exists in all possible worlds. (5,6)

So, since the actual world is a possible world, God exists. There are two possible counterarguments. One would be to deny premise 2, that is, to argue that the concept of God is incoherent. This is not clearly the case. The other would be to deny S5, since that is the only modal system under which the argument is valid. (In effect, this would be to say that the step to seven is invalid). Your argument regarding the fliminian is invalid. The necessarily existence of God is proved from the definition of God, not merely stipulated.

Why can't there be any more than one God? Well, God is by definition the greatest possible being. That is, for any being, if that being is not the greatest possible being, that being is not God. But if a being is the greatest possible being, it must have all the power which it is possible to have. If there are two beings, equal in power, they do not have all the power it is possible to have (since, if there was only one such being, it would have more power). Therefore, there can only be one greatest possible being. Finally, it is not possible for the greatest possible being to be evil, because it is better to be good than evil.

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