Confirmation holism

Confirmation holism, also called the Quine-Duhem thesis (after philosophers Willard Van Orman Quine and Pierre Duhem), is the claim a scientific theory cannot be tested in isolation; a test of one theory always depends on other theories and hypotheses.

The theory-dependence of observations

Suppose some theory T' implies an observation O:

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:T ightarrow O

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The required observation, however, is not made, therefore

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:sim O

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So by Modus Tollens,

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:sim T

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All observations make use of prior assumptions, which can be symbolised as:

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:O equiv left( p_1 wedge p_2 wedge p_3 cdots p_n ight)

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and therefore

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:sim O equiv sim left( p_1 wedge p_2 wedge p_3 cdots wedge p_n ight)

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which is by De Morgan's law equivalent to

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:sim left( p_1 wedge p_2 wedge p_3 cdots wedge p_n ight) equiv left( sim p_1 ee sim p_2 ee sim p_3 cdots ee sim p_n ight).

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In words, the failure to make some observation only implies the failure of at least one of the prior assumptions that went into making the observation. It is always possible to reject an apparently falsifying observation by claiming that only one of its underlying assumptions is false; since there are an indeterminate number of such assumptions, any observation can potentially be made compatible with any theory. So it is quite valid to use a theory to reject an observation.

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