Post Hoc Ergo Propter Hoc

The Latin term post hoc ergo propter hoc translates as “after this, therefore because of this,” is what is called a “logical fallacy.” This supposition of cause mistakenly assumes that a thing was caused by something else that occurred before. This is an example of correlation not being the same as causation. In other words, just because two things happened – one after the other – it does not mean that the first thing caused the second thing. To explore this concept, consider the following post hoc ergo propter hoc definition.

Definition of Post Hoc Ergo Propter Hoc


  1. An error in logic that assumes the cause of something is another thing that merely occurred earlier.


Unknown         Latin  (“after this, therefore because of it”)

What is Post Hoc Ergo Propter Hoc

Post hoc ergo propter hoc (referred to here as “post hoc“) refers to an error in logic, in which it is assumed that:

  • X happened before Y
  • Y happened, and was caused by something
  • Therefore, X caused Y

This type of thinking can be seen in superstition of old, as people took leaps of logic that ultimately did not make sense. For instance, in 1920, Martha saw a black cat crossing the road across from where she sat on her front porch. The baby she was carrying was born with a round, black spot on the back of her thigh. Martha knows, as everyone did at the time, that black cats are an evil omen, or an omen of bad luck – therefore, Martha knows that the black cat crossing the street caused her daughter’s birth mark.

Argument in Post Hoc Ergo Propter Hoc

Because post hoc refers to the mistaken assumption that one thing is caused by another specific thing, it can only exist when there is an argument – or something to compare. Simply put, just making a statement, such as “Sam is an idiot,” does not amount to post hoc fallacy – it’s simply a statement of opinion, whether it’s true or not.

As an example of post hoc ergo propter hoc, “Sam is a Raiders fan, so he’s an idiot” is a fallacy, as the statement draws a conclusion from something that is not related. Alternatively, “Sam didn’t load the truck properly, and the entire load shifted. Sam is an idiot,” may draw a relevant conclusion. This doesn’t necessarily make the argument or conclusion true, however.

Post Hoc Ergo Propter Hoc Examples

Post Hoc occurs when one jumps to a conclusion about causation, simply because there is some correlation between two events that occurred at the same time, or because one such event occurred just prior to the second.

As an example of post hoc ergo propter hoc, someone might reach the conclusion that, the larger a child’s shoe size, the better his handwriting. Therefore, having big feet makes writing easier. This is clearly a conclusion that is not based in fact. It may be true there is some correlation, but it’s not along a straight line. In fact, in order to determine why the child’s handwriting has improved, other factors must be considered.

Children’s feet grow larger as their bodies mature, making it necessary to increase their shoe sizes from time to time. Other developmental changes also occur as their bodies mature, including their coordination, which accounts for their improving handwriting and other skills.

Another example of post hoc ergo propter hoc might occur when Harold decides to do a little experiment to see what causes him to wake up with a bad headache after staying out drinking. Each night for a week, Harold consumes six drinks containing a different type of alcohol mixed with soda water. Scotch, gin, rum, vodka, tequila – each morning Harold woke up with a blazing headache, regardless of the type of alcohol he drank. Harold has an “Ah-ha moment” as he realizes that, as the only common ingredient in his drinks was soda water, it’s soda that was causing his headaches.

Correlation Does Not Imply Causation in GMO Foods

The phrase “correlation does not imply causation,” is bandied about in the statistical world to express the fact that just because two things happen to coincide, it does not mean one caused the other. In recent years, arguments, suppositions, and a lot of conjecture have surrounded the issue of Genetically Modified Organisms in the world’s processed foods, commonly referred to as “GMO foods.”

Such issues as climate change, increased frequency in natural disasters – drought, blight, floods, storms, volcanos – have made feeding the world’s rapidly increasing population more difficult. Genetically modifying certain plants and animals to produce more usable food parts, to resist disease, or to be drought-resistant, is the scientific community’s answer to the problem. For years, most people have been eating foods produced with ingredients from GMO food stuffs. Although producers of such foods claim they are perfectly safe, there are many people who believe these alterations are causing disease, such as cancer.

According to the National Cancer Institute (“NCI”), a division of the National Institutes of Health (“NIH”), it is undeniable that the incidence of a wide variety of cancers has risen greatly in recent decades. It is also true that the use of GMO foods has increased during that same time period. But there are so many factors in the world that are suspected, and some proven, to cause cancer, that it cannot responsibly be said definitively that GMO foods cause cancer.

In this example of post hoc ergo propter hoc, there are certain correlations between cancer rates and GMO usage, though this alone does not prove that GMOs cause cancer. The correlation does, however, invite more research.

Related Legal Terms and Issues

  • Causation – The ability of one variable to influence another; the act of causing something.
  • Correlation – A statistical relationship between two or more things or events.

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