Once again turning to Leibniz, Quine tries to explain synonymy by an
appeal to the notion of substitution salva veritate.
This not only seems to accommodate our initial instincts, but to allow synonyms to match each other vagueness for vagueness.
But we immediately notice that we need some provisos if this is to
work:
To solve the problem with the first pair, we will rule out substitution within the context of quotation marks. The second pair is handled by treating `bachelor buttons' as a single unit, word and disallowing substitution on the grounds that it would be like trying to substitute `feline' for `cat' is `catatonic.' But, note that both these solutions depend upon our simply taking notational conventions: quotation marks, word divisions at face value; we really have no reason to do so.
And there is another class of cases where substitution doesn't always work. Suppose that we grant that `dames' and `women' have the same meaning, it may nevertheless be the case that while
(a) I believe/know/hope that those women are ready to be seated
is true,
(b) I believe/know/hope that those dames are ready to be seated
is not, because while I assent to the sentence ``I believe/ know/ hope that those women are ready to be seated,'' I will not assent to I believe/ know/ hope that those dames are ready to be seated.
This class of sentences in which substitutivity seems to break
down--called intentional contexts--along with an even larger class
of what Quine calls opaque contexts, is not as easily solved
as the first two. But let's take all of them as resoluble, and see if
we can get what we want, which Quine now characterizes as
cognitive synonymy.