 As noted above, Duhem thought that the sort of underdetermination he had described presented a challenge only for theoretical physics, but subsequent thinking in the philosophy of science has tended to the opinion that the predicament Duhem described applies to theoretical testing in all fields of scientific inquiry. We cannot, for example, test an hypothesis about the phenotypic effects of a particular gene without presupposing a host of further beliefs about what genes are, how they work, how we can identify them, what other genes are doing, and so on. And in the middle of the 20th Century, W. V. O. Quine would incorporate confirmational holism and its associated concerns about underdetermination into an extraordinarily influential account of knowledge in general. As part of his famous (1951) critique of the widely accepted distinction between truths that are analytic (true by definition, or as a matter of logic or language alone) and those that are synthetic (true in virtue of some contingent fact about the way the world is), Quine argued instead that all of the beliefs we hold at any given time are linked in an interconnected web, which encounters our sensory experience only at its periphery: