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Post Hoc Ergo Propter Hoc |
| Description: | ||
| The argument offers an explanation that confuses co-occurrence with causality based on a temporal ordering of the events: A comes before B, so A causes B. In fact, the temporal ordering of the two events is likely to have been merely coincidental, or the result of some further causal factor. | ||
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| Comments: | ||
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| The phrase "post hoc ergo propter hoc" is a Latin phrase that means "after this, therefore because of this." | ||
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| Examples: | ||
| "Every time that rooster crows, the sun comes up. That rooster must be very powerful and important!" | ||
| "Nearly all heroin addicts used marijuana before they tried heroin. Clearly marijuana use leads to heroin addiction." | ||
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| Discussion: | ||
| Newton thought of cause and effect as sequential: a pool cue
must begin moving before it strikes a ball, which must move before it can
strike another ball, etc. When objects bump into each other, motion is
conveyed from one to another. Since motion takes place in time, cause and
effect must be temporally ordered. An effect can happen before the
cause only in science fiction stories involving time travel (which is
another way of saying, with apologies to Robert Heinlein, that it cannot
happen). So, when we try to offer explanations, it is appropriate to
take temporal ordering into account. It is just good reasoning to do so. The fallacy of Post Hoc takes temporal ordering into account. As such it appears to be a good piece of retroductive reasoning. Where, indeed, is the error? It is tempting to say that we discover the error only in retrospect. We formulate a hypothesis (based on a temporal ordering of events), and discover that it was not the best hypothesis only after we have done some further testing. But even good retroductive reasoning may result in the proposal of a false hypothesis. Guessing isn't guaranteed to be correct; even a good guess may be mistaken. If the fallacy of Post Hoc is to count as a fallacy, it cannot be only because the hypothesis later turns out to be wrong. Rather, it must be because it wasn't a very good guess in the first place. The fallacy of Post Hoc takes temporal ordering into account, but that is all it takes into account. It errs in overlooking other obviously relevant considerations, or in appealing to temporal ordering in a context in which other factors suggest that the mere sequence of events is not the most revealing consideration. |
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| Classification: A False Cause Fallacy (a retroductive fallacy of soundness with a falsehood in the major premiss). | ||
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| Source: The Port-Royal Logic (Antoine Arnauld and Pierre Nicole, L'Art de Penser, 1662) distinguishes this fallacy from the older 'non causa pro causa' fallacy. | ||
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