 One consequence of this general picture of human knowledge is that any and all of our beliefs are tested against experience only as a corporate body—or as Quine sometimes puts it, “The unit of empirical significance is the whole of science” (1951, p.  42).[4]  A mismatch between what the web as a whole leads us to expect and the sensory experiences we actually receive will occasion some revision in our beliefs, but which revision we should make to bring the web as a whole back into conformity with our experiences is radically underdetermined by those experiences themselves. If we find our belief that there are brick houses on Elm Street to be in conflict with our immediate sense experience, we might revise our beliefs about the houses on Elm Street, but we might equally well modify instead our beliefs about the appearance of brick, or about our present location, or innumerable other beliefs constituting the interconnected web—in a pinch we might even decide that our present sensory experiences are simply hallucinations! Quine’s point was not that any of these are particularly likely responses to recalcitrant experiences (indeed, an important part of his account is the explanation of why they are not), but instead that they would serve equally well to bring the web of belief as a whole in line with our experience. And if the belief that there are brick houses on Elm Street were sufficiently important to us, Quine insisted, it would be possible for us to preserve it “come what may” (in the way of empirical evidence), by making sufficiently radical adjustments elsewhere in the web of belief. It is in principle open to us, Quine argued, to revise even beliefs about logic, mathematics, or the meanings of our terms in response to recalcitrant experience; it might seem a tempting solution to certain persistent difficulties in quantum mechanics, for example, to reject classical logic’s law of the excluded middle (allowing physical particles to both have and not have some determinate classical physical property like position or momentum at a given time). The only test of a belief, Quine argued, is whether it fits into a web of connected beliefs that accords well with our experience on the whole. And because this leaves any and all beliefs in that web at least potentially subject to revision on the basis of our ongoing sense experience or empirical evidence, he insisted, there simply are no beliefs that are analytic in the originally supposed sense of immune to revision in light of experience or true no matter what the world is like.