Quine is led into these difficulties, I think, by an attempt to preserve the view which he, like Sellars, inherits from Carnap and ultimately from Wittgenstein’s Tractatus: the view that the world can be “completely described” in an extensional language. It is intensionality rather than intentionality which is the real bugbear, for only the non- truthfunctional character of intentional discourse makes its presumed subject more disreputable than, say, irreducibly biochemical talk of mitochondria.

Philosophy and the Mirror of Nature, Chapter 4