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Post hoc ergo propter hoc, Latin for "after this, therefore because (on account) of this", is a logical fallacy (of the questionable cause variety) which states, "Since that event followed this one, that event must have been caused by this one." It is often shortened to simply post hoc and is also sometimes referred to as false cause, coincidental correlation or correlation not causation. It is subtly different from the fallacy cum hoc ergo propter hoc, in which the chronological ordering of a correlation is insignificant.

Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality. The fallacy lies in coming to a conclusion based solely on the order of events, rather than taking into account other factors that might rule out the connection.



The form of the post hoc fallacy can be expressed as follows:

  • A occurred, then B occurred.
  • Therefore, A caused B.

When B is undesirable, this pattern is often extended in reverse: Avoiding A will prevent B.


From Attacking Faulty Reasoning by T. Edward Damer:[1]

"I can't help but think that you are the cause of this problem; we never had any problem with the furnace until you moved into the apartment." The manager of the apartment house, on no stated grounds other than the temporal priority of the new tenant's occupancy, has assumed that the tenant's presence has some causal relationship to the furnace's becoming faulty.

From With Good Reason by S. Morris Engel:[2]

More and more young people are attending high schools and colleges today than ever before. Yet there is more juvenile delinquency and more alienation among the young. This makes it clear that these young people are being corrupted by their education.

A class of examples is sometimes called the "Rooster syndrome", for "giving credit to the rooster crowing for the rising of the sun". The MMR vaccine controversy is a recent example of this logical fallacy, where the onset of autism symptoms follow childhood MMR vaccination but are not caused by it.[3]

See also


  1. ^ Damer, T Edward (1995). Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (3rd. ed.). Belmont, CA: Wadsworth Publishing. p. 131. ISBN 9780534217501. OCLC 30319422. 
  2. ^ Engel, S Morris (1994). With good reason: an introduction to informal fallacies (5th. ed.). New York: St. Martin's Press. p. 165. ISBN 9780312084790. OCLC 30478315. 
  3. ^ Fitzpatrick, Michael (2004). MMR and autism: what parents need to know. New York: Routledge. p. 83. ISBN 0-415-32178-6. 

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