Quine Against Propositions (and all intensional entities), by Schiffer:
1. Propositions exist only if "we have before us some standard of when to speak of
propositions as identical and when as distinct" (W&O p.200)
2. There is no such standard of individuation for propositions.
3. Therefore, propositions do not exist.
Argument for premise 2:
1. If there is a standard of individuation for propositions, it is to be given in terms of
the synonymy relation for sentences. (I.e., if we can make sense of that relation,
we can say that proposition p = proposition q iff two sentences are synonymous if
one means p and the other means q.)
2. There is such a standard only if we can define that relation in non-intentional
terms.
3. We can define synonymy in non-intentional terms only if we can define it in
terms of dispositions to verbal behavior (for that's all we ultimately have to go on
in figuring out what others mean by their words).
4. But we cannot so define synonymy: “The totality of dispositions to speech
behavior is compatible with alternative systems of sentence-to-sentence
translations so unlike one another that translations of a standing sentence under
two such systems can even differ in truth value" (W&O p.207)
5. Therefore, there is no standard of individuation for propositions.
Quine's thesis of the indeterminacy of radical translation: There can be no such thing as
the correct translation manual of a radically alien language into one's own language; for
whatever translation manual one comes up with, there will always be another that is
equally correct but that maps the alien sentences onto sentences of one's own language
that, by any remotely possible rendering of synonymy, are not synonymous with those
the first manual maps on to one's own sentences—they needn't even have the same truth
values.