Firmitas

Cum Hoc Ergo Propter Hoc

Revision 1
© 2011-2019 by Zack Smith. All rights reserved.

Cum Hoc Ergo Propter Hoc

This is a fallacy in which a person thinks that a concurrent event caused some outcome, simply because it happened at the same time.

Its form
  • Event A happens around time T.
  • Event B happens around time T.
  • Therefore A caused B.

Examples

A person was seen walking along a road at 5am. A car was stolen along that road sometime in that morning. Therefore the person stole the car.

A boy asked a girl to pull on his finger, and just as she pulled it, the boy farted loudly. Therefore the girl's pulling of the finger caused the fart.

Weaknesses

The arguer is making the mistake of deciding that a particular concurrent event A, rather than any others events, concurrent or prior, caused some event or outcome B. You need only ask: Haven't you considered that something else might have caused B, rather than A? There is a lack of imagination.

Event A could be completely irrelevant to B, or unable to affect anything. For example, a preacher puts his hand on the forehead of a believer and speaks some nonsense. If the believer concurrently thinks he is being healed of an illness, he is surely deluded.

It may be, as if often the case, that a complex interaction of events is causing event B. You can attack the simplistic view that only one influence caused B.