The Ontological Argument - valid or debunked?

[SteveII]

I still have a problem with the claim that maximal greatness is subjective. We are not talking about the greatest being we can imagine. We are talking about the greatest being possible. Even if a complete picture of what that might mean is unclear, it does not matter.

What makes a specific property objectively great?  If properties are objectively great or objectively bad, then you should be able to tell me what makes any specific property great or bad.  But as I noted with Chad, properties do not form an ordered set from bad to good.  You cannot rank any one property as being better or worse to possess except by subjective opinion.  Therefore you can't rank necessarily existing as being better or worse than any other property aside from personal preference.

It does not matter what we discern to be a great making property--that would be subjective. As Anselm put it: by definition, there cannot be anything greater than God. You might object what is the purpose of defining God this way if we don't know what it means. Well, depending on your purposes in discerning what God is like, you can look at scripture or natural theology (or both) as a kind of control.

I mentioned this back a few pages: The difference is between epistemic possibility and metaphysical possibility. Epistemic possibility is simply "for all we know something is possible". On the other hand, to illustrate metaphysical possibility take a math equation 24673244/8=3005567. While we might say "for all we know" this might be true, but if it is true, than it is necessarily true if it is false than it is necessarily false. If a maximally great being exists, it exists necessarily in a metaphysical sense. Therefore, God’s existence is either possible or impossible.

Why?  Because you think a maximally great being would have that property?  You're still just tacking on 'exists necessarily' to a list of arbitrary attributes.  A maximally great being is not like a mathematical equation except in the sense that it cannot be coherently and objectively defined, as some math equations are.  1/0=3 is simply undefined because you cannot divide by zero.  It is neither true nor false, it is simply not defined to have a value.  Simply asserting that a maximally great being must be metaphysically necessary is nothing more than you stating your preference that, if you were a great being, you would desire to be metaphysically necessary.  And the question is why?  What is it about existing necessarily that makes it desirable?  Is it an objective feature of necessarily existing that makes it desirable?

I would be interested to hear your thoughts on Plantinga's defense of his formulation (from wikipedia): The conclusion relies on a form of modal axiom S5, which states that if something is possibly true, then its possibility is necessary (it is possibly true in all worlds). Plantinga's version of S5 suggests that "To say that p is possibly necessarily true is to say that, with regard to one world, it is true at all worlds; but in that case it is true at all worlds, and so it is simply necessary."