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A post hoc fallacy is a logical fallacy, a statement that appears correct on its surface but does not hold up on deeper examination. “Post hoc” is short for post hoc, ergo proper hoc, a Latin phrase meaning “after this, therefore because of this.” It presumes that because one event occurs after another, the first event must have caused the second event. This is the foundation for many superstitions and spurious beliefs from prehistory to the present. In reality, there may be no cause-and-effect relationship between the two events.
Logic is the science of distinguishing factual information from supposition and unfounded belief. Logical fallacies are common misconceptions that are nonetheless regarded as true by large groups of people. These generally fall into certain widely recognized categories. The study of logic is thousands of years old; consequently, many logical fallacies are named in Latin, which was once the language of scientific and legal discourse.
The post hoc fallacy is a very common kind of misconception. Most people discover the law of cause and effect at a very young age. Since a cause always precedes its effect, this can lead to the mistaken notion that a given event caused a following event, when the relationship between the two events may be different or entirely nonexistent. A classic illustration is known as the rooster syndrome; roosters commonly crow at dawn, preceding the sunrise. A primitive society or a child might therefore believe the rooster’s crow causes the sun to rise.
Many rituals, traditions, and beliefs have been created as a result of the post hoc fallacy. Primitive societies, witnessing a solar eclipse, often performed elaborate rituals to “bring the sun back.” When the sun did return, they concluded their rituals were successful and decided to practice them at every eclipse. Faith healers and other magical remedies have often benefited from this fallacy when their work seemed to produce beneficial results in ill or injured subjects. In reality, the recovery was probably due to the subject’s immune system and natural healing capacity.
The post hoc fallacy, however, is not limited to primitive cultures. Many modern-day superstitions result from this kind of misconception. Amateur and professional athletes may decide that an item or article of clothing is a lucky charm if they wore it during a particularly successful game. In political discourse, pundits and elected officials often indulge in post hoc fallacies when they quote anecdotal evidence to promote or discredit a particular policy. Anything that does not support this argument, including actual scientific evidence, is accidentally or deliberately ignored.