In "Carnap and Logical Truth," Quine makes the following argument (expanded by Harman in his 1967 article "Quine on Meaning and Existence: I" in Review of Metaphysics
"Consider... the logical truth 'Everything is self-identical'... We can
say that it depends for its truth on traits of the language (specifically on the usage of '='), and not on the traits of its subject matter; but we can also say, alternatively, that it depends on an obvious
trait, viz. self-identity, of its subject matter, viz. everything. The tendency of our present reflections is that there is no difference."
(Carnap Library of Living Philosophers volume, p.390)
I think, contra Quine, that there might be a clear difference. To say that one thing (e.g. the truth-value of a sentence) depends on
another (e.g., the traits of a language, or the traits of its subject matter) usually means that changing the second can change the first; the first is sensitive to changes in the second. E.g. thermometer readings depend on ambient temperature: as the ambient temperature changes, the readings change. This is not
to say that 'X depends on Y' means that every
change in Y will have a corresponding change in X (that would be perfect correlation), but it does
require that there must be some
change in Y that results in a change in X. If X stays the same no matter what values Y takes, then X does not depend on Y.
Now think about Quine's (English) sentence 'Everything is self-identical.' If we were to vary the traits of the language in which this is written, e.g. by letting 'self-identical' mean not self-identical
, then the sentence would be false. This shows that (as Quine happily admits elsewhere) the truth-value of a sentence does depend on the traits of the language in which it is expressed.
But now think about varying the traits of the subject-matter of this sentence, 'viz., everything,' or the world, or however you want to think about it. Assuming we hold the meanings of the words fixed, there is no possible way the world can be that would change the truth-value of this sentence. That is, there is NO change in the way the world is that would change the truth-value of this sentence. (In logic-ese, the sentence is true in all models.) Thus, if the above characterization of dependence is right, then the truth-value of 'Everything is self-identical' does not
depend on the traits of its subject matter, viz. everything.