6: Post Hoc Fallacy

Informal Fallacies

Key Terms

Modus Ponens
Modus Tollens
Disjunctive Syllogism
Reduction Fallacy
Post Hoc Ergo Propter Hoc

  • Not logical
  • Pseudo-reasoning (false reasoning)
  • Unsound arguments

Fallacies of Cause

  • Deny, confuse, or falsify the cause related to an argument
  • Four types:
    • Reduction fallacy
    • Post hoc ergo propter hoc
    • Texas Sharpshooter fallacy
    • Tautology

Post Hoc Ergo Propter Hoc

  • Latin phrase that means “after this, therefore because of this.”
  • Often shortened to Post hoc 
fallacy. It is also called false cause or correlation not causation
  • The structure or form of a post hoc fallacy is: 

Post Hoc Fallacy

This occurred. Then that occurred.
Therefore this caused that.


  • We won the game! I’m never washing these socks again!

  • There is an increase in college enrollment and crime. Therefore, college enrollment causes crime.


  • Conclusions drawn from insufficient information
  • This fallacy assumes causation when in fact there may be no connection
  • Particularly hazardous in research and debate