The Ontological Argument - valid or debunked?

[SteveII]

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.

What I object to is not that an MGB cannot be constructed in practice, but that an MGB cannot be constructed in principle.  Let us suppose that we have a possible world populated only by demons.  Things that you might postulate as great making they might postulate as bad making.  Evil preferred to good.  No necessarily existing good God.  Certainly no omnipotent overlord.  Demons just want to have fun.  There is nothing that makes 'good' necessarily greater than evil.  It is neutral, outside of itself.  So it wouldn't be a great making property, it would just be an optional, accidental element.  Incorporating 'good' into the description of an MGB would just be arbitrary.  So there's no objective reason an MGB would have this or any other property.  All properties are metaphysically neutral.  No one property is any 'greater' than any other.  So an MGB would not necessarily have any particular set of properties.  That's the crux of the matter.  Not that an MGB would be subjective, but that no set of properties -- no properties at all -- are inherently good or bad.  If no particular property is either good or bad -- they're neutral -- what sense can one make of a maximally great being?  It makes no sense.  It can't be defined because real properties are neither good nor bad.  Great making properties form an empty set.  It's not that greatest is inscrutable because of our subjectivity, it's incoherent because there is no such thing as objectively greatest.

Thank you for you answer above. I understand your position. I still think the tri-omni characteristics are part of any MGB description. Even if we do not know exactly what they are, we intuitively know they are great-making properties. I would like to point out that with other natural theology arguments like the Moral Argument and the Cosmological argument at the very least can provide insight into what characteristics a MGB may have (enough anyway to begin to remove the subjectivity of the description). 

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."

I think it's a form of begging the question.  Once you define something, anything, as necessarily existing, then unless it is logically contradictory, you are declaring that it exists.  Modal logic here is simply dressing up the assertion that an MGB would by definition be necessary.  As noted, because of the problem that great making properties don't exist as such, one cannot assert that a great being would have this or that great making property.  The assignation of properties then becomes merely arbitrary assertion.  As stated, making that particular arbitrary assertion is tantamount to claiming the entity exists and thus begs the question.

I don't think it is question begging. Through inductive reasoning you conclude that a MGB would be necessary. It is not an arbitrary property assigned to trigger the modal logic. 

I understand if you grow tired of this. No hard feelings if you don't want to continue.