Full Idea
It is because Quine holds constant singular terms to be always eliminable by an extension of Russell's theory of definite descriptions that he takes the bound variables of first-order quantification to be the sole means by which we refer to objects.
Gist of Idea
Quine rests existence on bound variables, because he thinks singular terms can be analysed away
Source
report of Willard Quine (On What There Is [1948]) by Bob Hale - Necessary Beings 01.2
Book Reference
Hale,Bob: 'Necessary Beings' [OUP 2013], p.11
A Reaction
Hale defends a Fregean commitment to existence based on the reference of singular terms in true statements. I think they're both wrong. If you want to know what I am committed to, ask me. Don't infer it from my use of English, or logic.