The difficulty that Carnap encountered shows that reductionism is, at best, unproven and very difficult to prove. Until a reductionist can produce an acceptable proof, Quine maintains that reductionism is another "metaphysical article of faith". Quine's holism Instead of reductionism, Quine proposes that it is the whole field of science and not single statements that are verified. All scientific statements are interconnected. Logical laws give the relation between different statements, while they also are statements of the system. This makes talk about the empirical content of a single statement misleading. It also becomes impossible to draw a line between synthetic statements, which depend on experience, and analytic statements, that hold come what may. Any statement can be held as necessarily true according to Quine, if the right changes are made somewhere else in the system. In the same way, no statements are immune to revision. Even logical laws can be revised according to Quine. Quantum logic, introduced by Garrett Birkhoff and John von Neumann, abandons the law of distributivity from classical logic in order to reconcile some of the apparent inconsistencies of classical Boolean logic with the facts related to measurement and observation in quantum mechanics. Quine makes the case that the empirical study of physics has furnished apparently credible grounds for replacing classical logic by quantum logic, rather as Newtonian physics gave way to Einsteinian physics. The idea that logical laws are not immune to revision in the light of empirical evidence has provoked an intense debate (see "Is Logic Empirical?"). According to Quine, there are two different results of his reasoning. The first is a blurring of the line between metaphysics and natural science. The common-sense theory about physical objects is epistemologically comparable to the gods of Homer. Quine is a physicalist, in the sense that he considers it a scientific error not to adopt a theory which makes reference to physical objects. However, like Gods of Homer, physical objects are posits, and there is no great epistemic difference in kind; the difference is rather that the theory of physical objects has turned out to be a more efficient theory. As Quine states in "Two Dogmas", "The myth of physical objects is epistemologically superior to most in that it has proved more efficacious than other myths as a device for working a manageable structure into the flux of experience". The second result is a move towards pragmatism. Since,