W.V.O. Quine, answered from the texts and cited to the page.
Confirmation holism is the thesis that empirical statements do not face the tribunal of experience individually; they face it in groups — typically as components of a larger theoretical structure. The Duhem-Quine thesis names the structural insight that any test of a hypothesis is a test of the hypothesis conjoined with auxiliary assumptions, and that empirical disconfirmation can in principle be absorbed by adjusting any of the conjoined claims rather than by giving up the target hypothesis.
The web of belief metaphor — knowledge as a fabric whose periphery is touched by experience but whose interior is shielded by intervening adjustments — captures the structure. Within the web, the maxim of minimum mutilation governs which adjustments to make: prefer the revision that leaves the most of our prior commitments intact, all else equal.12345
So he looks to his theory with a critical eye. Over-logicizing, we may picture the accommodation of a failed observation categorical as follows. We have before us some set of beliefs that was found jointly to imply the false categorical. Implication may be taken here simply deducibility logic truth functions, quantification, and identity.Confessions of a Confirmed Extensionalist, pp. 380–381
The other requirement intersubjectivity; witnesses event prepared agree their verdict, provided pertinent technical vocabulary and their sensory receptors are in order. Prediction of observable events, then, is the test of science. It is how scikeeps contact subject matter, namely, the world.Confessions of a Confirmed Extensionalist, pp. 167–168
In that situation, the falsity of the observation categorical does not conclusively refute the hypothesis. What it refutes is the conjunction of sentences that was needed to imply the observation categorical. In order to retract that conjunction we do not have to retract the hypothesis in question; we could retract some other sentence of the conjunction instead. This is the important insight called holism.Pursuit of Truth, pp. 23–24
This asymmetry is pure logic: what implies a truth may be true or false, but what implies a falsehood is false. It would appear to be easier, therefore, to refute a false hypothesis than to establish a true one. If a hypothesis implies observations at all, we may stand ready to drop the hypothesis as false as soon as an observation that it predicts fails to occur.The Web of Belief, pp. 111–112
If the false categorical is still implied, we try rescinding both. We continue thus until the implication is defused. But this is only the beginning. We must also track down sets of sentences elsewhere, in our overall theory, that imply these newly rescinded beliefs; for those must be defused too. We continue thus until consistency seems to be restored.Pursuit of Truth, pp. 24–25
Confirmation holism is one of the most influential doctrines in mid-twentieth-century philosophy of science. The Duhem-Pierre antecedent (1906) and the Quine extension in 'Two Dogmas' (1951) together constitute the Duhem-Quine thesis. Jerry Fodor and Ernest Lepore's Holism: A Shopper's Guide (Blackwell, 1992) mounted the most extensive contemporary critique on behalf of molecularism — the position that meaning and confirmation depend on local clusters of beliefs rather than on the entire web. The contemporary Bayesian-confirmation tradition (Earman, Maher) engages the holism in a more formal idiom. The position remains contested.