Post hoc ergo propter hoc - A distinguished professor observing a series of events where a butterfly's wing flap appears to lead to a distant tornado.

Post Hoc Ergo Propter Hoc

Post hoc ergo propter hoc describes a causal fallacy.  It was made popular by that erstwhile American political period drama called ‘The West Wing’!

Post hoc ergo propter hoc is a logical misconception where someone argues that one event happens because another event happened before it, and the earlier event caused the second event. By means of an illustration:

  • A happened before B.
  • Therefore, A is the cause of B.

Now, if you want a totally bonkers example of post hoc ergo propter hoc fallacy:

  • After I sneezed, then suddenly my laptop exploded.
  • Therefore, my sneezing caused my laptop to explode.

or just to make sense of the cartoon:

  • A butterfly flapped its wings and then a tornado appeared.
  • Therefore, the butterfly caused the tornado.


Post hoc ergo propter hoc
Water Kills!

Post hoc ergo propter hoc poorly, but trivially translates from Latin as ‘after this, therefore because of this’. Now, developing that train of thought, let’s examine the case of water… as we all know: water kills!  Not only does it kill, it can do a lot worse!  For example:

  • 100% of all murders and drug dealers openly admit to drinking water
  • Over consumption of water can cause excessive urine, sweating and even death.
  • Water is one of the main ingredients in pesticides
  • Water is the leading cause of drowning
  • 100% of all people who drink water will die.

Those are all examples of post hoc ergo propter hoc fallacies applied to water. Yes, of course, those are ridiculous examples, but they are there to illustrate the fallacy and like most illustrations they are designed to be somewhat ridiculous or at the very least eye catching.  Of course there is a much more serious side to it.  Take for example the issue of vaccine hesitancy, fundamentally the reluctance or outright refusal to be vaccinated or, more critically, to have children vaccinated against contagious diseases despite the availability of a vaccination.  The World Health Organization identify it as one of the top ten global health threats.

Arguments against vaccination are contradicted by overwhelming scientific consensus about the safety and efficacy of vaccines.  This is where the post hoc ergo propter hoc  fallacy is illustrated.  People see others diagnosed with illnesses shortly after receiving vaccinations, and assume that the vaccination caused the illness.