This post is an addendum to A Tension in Quine's Theory of Existence. Go there for all the scholarly niceties and references.
The present post is in part a response to a comment by Peter Lupu.
Suppose you tell me that for a to exist is for a to be identical to something: a exists =df (Ex)(x = a). Then I say this is either circular, or self-contradictory, or trivial.
Circular. Suppose the domain of quantification contains only existing individuals, and no Meinongian indviduals: individuals that
actually have properties but do not exist. Then for
a to exist is for
a to be identical to something that exists. From this, however, I learn precisely nothing about what it is for an individual to exist. I learn nothing because the explanation moves in a circle of embarrassingly short 'diameter.'
You may wonder what it would be for an account of existence NOT to be circular. Well, suppose you tell me that for a to exist is for a's ontological constituents to be unified. That is not circular since you are explaining the existence of a in terms of other, more fundamental, items. That explanation raises its own questions and may be worthless for other reasons; but it is not worthless because circular. Quine's explication, however, is worthless because circular.
Self-Contradictory. Suppose now that the domain contains only nonexistent individuals. Then for a to exist is for a to be identical to something that does not exist. That, clearly, is self-contradictory. Obviously, it does no good to say that the domain contains both existent and nonexistent individuals. For there to be a connection between existence and the particular quantifier it must presupposed that the domain consists of existents only. But then the circularity objection kicks in.
Trivial. "You are just not getting it. Quine is not trying to explain or explicate singular existence. His concern is merely with singular existentials. He is merely providing a way of translating sentences of the form a exists into his preferred notation."
Then what Quine has to say is of no interest to ontology and we may pass it by.
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