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Canceling Hypotheses |
| Description: | ||
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| The argument defends one hypothesis by proposing a second hypothesis to explain why certain events predicted by the first hypothesis did not occur. The second hypothesis cancels or undermines the predictions made by the first hypothesis. | ||
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| Comments: | ||
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| Conspiracy theories are a particularly important example of this fallacy. One hypothesis offers an explanation (for which there is no evidence), and a second hypothesis explains the lack of evidence by suggesting that someone has taken steps to cover up or destroy the evidence. | ||
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| Examples: | ||
| "Based on a theory that brain size would have some correlation with personality, Paul Broca predicted that criminals would have smaller average brain size than non-criminals. Weighing of brains failed to support this hypothesis, but Broca noted that the criminals in his study had died violent deaths, while the non-criminals had died of long illnesses--long illnesses, during which their brains had diminished in size." | ||
| "Strange lights and unusual military activity around Roswell, New Mexico, in 1947 were due to a crash landing (or possibly even shooting down) of an alien spacecraft. The government denies that this is so, and is covering up the evidence so the public will not panic." | ||
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| Discussion: | ||
| Sometimes, of course, there are factors that hide evidence.
Much evidence about ancient civilization has been destroyed by
grave-robbers, for example. The fossil record is notoriously incomplete.
Sometimes there are even intentional cover-ups, as when Nixon's staff hid
evidence of the Watergate break-in. However, we discover what factors are
responsible for hiding evidence by looking at other evidence.
Eventually we must expect evidence to come to light -- even evidence of a
cover-up.
Remember that a fallacy is not defined as an argument with a false conclusion, but an argument that we should not find to be persuasive since it runs a high risk of having a false conclusion. Sometimes evidence is destroyed or hidden. Hence, sometimes, a pair of canceling hypotheses can turn out to be true. But it is a risky pattern of reasoning. It should be avoided, unless genuine evidence of a cover-up or other evidence-destroying event can be provided. |
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| Classification: A retroductive Fallacy of Circularity | ||
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| Source: I first became aware that this was an important fallacy in scientific reasoning from reading Stephen Jay Gould's The Mismeasure of Man, New York: Norton, 1981. I coined the ugly term "canceling hypotheses." The term "conspiracy theory" is catchier, and has greater popular currency (see, for example, the movie of that title starring Mel Gibson), but it must be remembered that not all instances of this fallacy involve a conspiracy. | ||
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