In his latest installment, London Ed writes:
Ed thinks that the assumption that the domain of quantification is a domain of existing individuals is a contingent assumption. But I didn't say that, and it is not. It is a necessary assumption if (1) [namely that ‘Island volcanos exist’ is logically equivalent to ‘Some volcano is an island.’] and sentences of the same form are to hold. [My emphasis]
But he then says that there is nothing in the nature of logic to stop us from quantifying over nonexistent individuals, which I don't follow at all. We start with the initial logical or definition[al] assumption about the meaning of the verb 'exists'.
(1) 'A golden mountain exists' = 'Some mountain is golden.'
[. . . ]
I suppose I need to explain why there is nothing in the nature of logic to stop us from quantifying over nonexistent individuals. There would be something to stop us if the notion of a nonexistent object were logically self-contradictory. But I see no contradiction in it. So let me put the question to Ed: Do you think that the very idea of a nonexistent object is logically self-contradictory? If you do think this, then I refer you to my November 2009 post, Is Meinong's Theory of Objects 'Obviously Self-Contradictory'? Van Inwagen Says 'Yes.'
There is also the issue of question-begging. Ed needs to justify the slide from
a. 'A golden mountain exists' is logically equivalent to 'Some mountain is golden'
1. 'A golden mountain exists' = 'Some mountain is golden.'
Equivalence is not identity! Not even logical equivalence is identity. Propositions p, q are logically equivalent iff there is no logically possible world in which p is true and q false, or vice versa. Now Ed and I agree about (a). But the inference from (a) to (1) is invalid. Consider triangularity and trilaterality. There is no logically possible world in which it is true that something is triangular but not true that something is trilateral. So 'Something is triangular' and 'Something is trilateral' are logically equivalent. But it doesn't follow that they express the same proposition or that the triangularity = trilaterality.
Likewise, it does not follow from (a) that existence = someness. Every world in which cats exist is a world in which something is a cat. No doubt. But how is it supposed to follow that the 'property' of existence is identical to the syntactical 'property' expressed by *Some ___ is a ---*?
Ed begs the question against me by simply stipulating that the meaning of the verb 'exists' shall be identical to the meaning of 'Some ___ is a --.' That is what I deny.