Affirming the consequent

The false argument that, because the consequence of a conditional proposition is true, the antecedent must also be true. For example, inferring from “If this theory or belief is true, x is true” that “x is true, so this theory is true”: if photographic film is (inadvertently and prematurely) exposed, photographs taken with the film won’t develop as they should – the photographs taken on this film haven’t come out properly, so the film has been accidentally exposed. There are other, alternative explanations which would account for why the photographs taken did not come out, for example, the lens cap may have been left on the camera when the photos were taken, etc. Or if there’s psi activity, then the experimental data will deviate from chance. The data collected so deviates: consequently, we have good evidence for (or ‘proof’ of) psi! Needless to say, there are other explanations available for any such claimed effects.

(see also: denying the antecedent, Fallacy)

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