Post Hoc: Definition and Examples of the Fallacy

Glossary of Grammatical and Rhetorical Terms

Man sitting on rock with picnic baskets
Eula Becker's presence at the picnic didn't cause the rain. Johner Images/Getty Images

Post hoc (a shortened form of post hoc, ergo propter hoc) is a fallacy in which one event is said to be the cause of a later event simply because it occurred earlier. Also called the fallacy of false cause, faulty cause, and arguing from succession alone.

"Although two events might be consecutive," says Madsen Pirie in How to Win Every Argument (2015), "we cannot simply assume that the one would not have occurred without the other."

The Latin expression post hoc, ergo propter hoc can be translated literally as "after this, therefore because of this."

Examples and Observations

  • The Cause of Malaria
    "Malaria was for centuries a baffling plague. It was observed that persons who went out at night often developed the malady. So, on the best post hoc reasoning, night air was assumed to be the cause of malaria, and elaborate precautions were taken to shut it out of sleeping quarters. Some scientists, however, were skeptical of this theory. A long series of experiments eventually proved that malaria was caused by the bite of the anopheles mosquito. Night air entered the picture only because mosquitoes preferred to attack in the dark."
    (Stuart Chase, Guides to Straight Thinking. Harper, 1956)
  • iPods and Violent Crime
    "The Urban Institute, a research organization based in Washington, has released an interesting report that suggests that the proliferation of iPods helps account for the nationwide rise in violent crime in 2005 and 2006.

    "The report suggests that 'the rise in violent offending and the explosion in the sales of iPods and other portable media devices is more than coincidental,' and asks, rather provocatively, 'Is There an iCrime Wave?'

    "The report notes that nationally, violent crime fell every year from 1993 to 2004, before rising in 2005 and 2006, just as 'America’s streets filled with millions of people visibly wearing, and being distracted by, expensive electronic gear.'

    "Of course, as any social scientist will tell you, correlation and causation are not the same thing."
    (Sewell Chan, "Are iPods to Blame for Rising Crime?" The New York Times, September 27, 2007)
  • Eula Becker and Rain
    "'Next comes Post Hoc. Listen to this: Let’s not take Bill on our picnic. Every time we take him out with us, it rains.'

    "'I know somebody just like that,' [Polly] exclaimed. 'A girl back home--Eula Becker, her name is. It never fails. Every single time we take her on a picnic--.'

    "'Polly,' I said sharply, 'it’s a fallacy. Eula Becker doesn’t cause the rain. She has no connection with the rain. You are guilty of Post Hoc if you blame Eula Becker.'

    "'I’ll never do it again,' she promised contritely."
    (Max Shulman, The Many Loves of Dobie Gillis. Doubleday, 1951)
  • The Hat Joke and Losing Texas
    President Bartlet: Twenty-seven lawyers in the room, anybody know “post hoc, ergo propter hoc"? Josh?
    Josh: Uh, uh, post, after, after hoc, ergo, therefore, after hoc, therefore, something else hoc.
    Bartlet: Thank you. Next?
    Josh: Uh, if I’d gotten more credit on the 443 . . .
    Bartlet: Leo?
    Leo: After it, therefore because of it.
    Bartlet: After it, therefore because of it. It means one thing follows the other, therefore it was caused by the other, but it’s not always true. In fact, it’s hardly ever true. We did not lose Texas because of the hat joke. Do you know when we lost Texas?
    C.J.: When you learned to speak Latin?
    Bartlet: Go figure.
    (Aaron Sorkin, "Post Hoc Ergo Propter Hoc," The West Wing, 1999)