Published on

Cause and Effect fallacies

  • avatar
    Carlos Baraza
    I write software and other philosophical stuff.

Lately, I have been learning about formal and informal logic. Today, I will share some notes on cause-effect related fallacies, which are unfortunately very common in arguments.

Post hoc, ergo propter hoc

Just because B happens after A, it doesn't mean that A caused B.


  • My car has been working for 10 years. It just stopped working after I lent it to you last week, therefore you broke it.

Neglect of a common cause

A and B are correlated. It doesn't mean A causes B or B causes A. There could be a third reason C causing both.


  • Two symptoms happen in the same patient, but both are caused by a third condition.

Causal oversimplification

Take one factor and reach a conclusion using that only reason, ignoring all the other contributing factors.

Confusing of a necessary and a sufficient condition

Condition A is necessary for B if you can not have B without having had A.

  • Oxygen is necessary for fire. This does not mean that everywhere there is oxygen there will also be fire.

Condition A is sufficient for B if anytime there is B, there has also been A.

  • Winning lottery is sufficient to become a millionaire. But not necessary to become a millionaire, as there are other ways.


  • I don't understand why the plant died. I watered it.
  • Watering the plant is necessary but not sufficient.

Slippery slope fallacy (domino effect)

One small thing can follow a succession of fatal cause-effect chain, leading to a bad outcome.


  • For want of a nail the shoe was lost.For want of a shoe the horse was lost.For want of a horse the rider was lost.For want of a rider the message was lost.For want of a message the battle was lost.For want of a battle the kingdom was lost.And all for the want of a horseshoe nail.
  • One sip of beer can lead to wine, then to liquor, then to marijuana, then to heroin and then to the total ruin. Therefore, put down that drink.
  • This sets a dangerous precedent...

This topic is really interesting to me and I will continue to explore other fallacies and human biases in the future.