How do we know that Wyman and McX aren't the same person?

Question

Quine thought that only that which exists can be referred to, or in other words 'to be is to be the value of a bound variable'.

However, what of his equally famous fictional characters Wyman and McX? If we cannot really refer to nonexistent entities, then in what way is the reader meant to understand Wyman and McX?

More generally (and more to the point beyond rhetorical speech), does Quine consider the possibility that the fictional subjects we quantify over aren't a mysterious subdivision of 'existents'?

One of his criticisms of the Meinongian account of fictional entities is that it requires talking about 'being' in a mysterious and unclear way.

But couldn't we just postulate that the mind has the ability to quantify over nonexistents?

Why should our ability to imagine something nonexistent at the present moment and quantify over it immediately qualify the Meinongian suggestion that this subject being quantified over is itself qualified as a sort of diminished existent?

In other words, why must we believe that the only two approaches to referencing a nonexistent is the Quinean minimalism which holds the whole operation to be a farce and the Meinongian postulation which paradoxically attributes existence to nonexistents?

Perhaps what is immediately referenced in our language and logic is existentially impartial, like a mental form void of existence outside of its pure dependence on mental activity. The fictional entity (the mental form) as a fictional entity does not have being whereas our concept of the fictional entity (our mental activity) as a concept does.

Answer 1

In other words, why must we believe that the only two approaches to referencing a nonexistent is the Quinean minimalism which holds the whole operation to be a farce and the Meinongian postulation which paradoxically attributes existence to nonexistents?

No, you are correct. These are not the only two approaches to the existence of fictional objects.

This SEP article contains a review of contemporary positions and arguments, regarding fictional (imaginary) objects. Four main positions are discussed:
Possibilism: fictional objects are possible entities,
Meinungianism: fictional objects are actual entities,
Creationism: fictional objects are author dependent entities,
Anti Realism: fictional objects are not entities (they do not exist).

Russell's approach, and Quine's in his footsteps, fall under anti-realism concerning fictional objects. So there are (at least) two extant approaches to fictional objects beside Russell's (= Quine's) and Meinung's.

The fictional entity (the mental form) as a fictional entity does not have being whereas our concept of the fictional entity (our mental activity) as a concept does.

The existence of the concept does not seem to be a solution, because it is undisputed from the start. The question is whether (e.g.) Batman himself exists in some sense, not just the concept of Batman.

Quine's use of the fictional philosophers Wyman and McX is, to my mind, an embarrassment. If one cannot name real philosophers holding some position, then the position one criticizes is often a mere straw man.

Answer 2

Your question relates to a more general one concerning the existence of fictional entities, which Quine deals with in the same paper (On What There Is).

Briefly, Quine says that names of fictional entities are not names that refer but rather are descriptions, that function like predicates. So, for example, "Pegasus has wings" should be taken as "there is something which has the property of being pegasus, and for anything that has this property also has wings", which does not refer to anything explicitly.

The exact same treatment would apply to the fictional McX and Wyman.