Post hoc ergo propter hoc

From Wikipedia, the free encyclopedia
  (Redirected from Post hoc)
Jump to: navigation, search
"Post hoc" redirects here. For the analytical technique, see Post-hoc analysis.
For the West Wing episode, see Post Hoc, Ergo Propter Hoc (The West Wing).

Post hoc ergo propter hoc (Latin: "after this, therefore because of this") is a logical fallacy (of the questionable cause variety) that states "Since event Y followed event X, event Y must have been caused by event X." It is often shortened to simply post hoc. It is subtly different from the fallacy cum hoc ergo propter hoc ("with this, therefore because of this"), in which two things or events occur simultaneously or the chronological ordering is insignificant or unknown. 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 following is a simple example:

The rooster crows immediately before sunrise, therefore the rooster causes the sun to rise.

Pattern[edit]

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.

Examples[edit]

  • "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, holds that the tenant's presence has some causal relationship to the furnace's becoming faulty.[1]
  • In the obsolete theory of spontaneous generation, people once erroneously believed that maggots arose spontaneously from rotting meat, due to observing their presence at the site of rotting meat. Francesco Redi disproved this by using jars with lids permeable to air but not insects, compared to uncovered jars. The maggots could only enter the uncovered jars.

See also[edit]

References[edit]

  1. ^ Damer, T Edward (1995). Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (3rd. ed.). Belmont, CA: Wadsworth Publishing. p. 131. ISBN 978-0-534-21750-1. OCLC 30319422.