Post Hoc, Mere Correlation & Oversimplified Cause Fallacies

Instructor: Jason Nowaczyk

Jason has a masters of education in educational psychology and a BA in history and a BA in philosophy. He's taught high school and middle school

The following lesson will cover assumptions we make about causation. We call these assumptions fallacies of causation. A short quiz will follow the lesson to check for your understanding.


By nature, human beings are curious creatures. We're always looking for the causes of things. However, if we're not careful, we may mistakenly attribute the causes of events to things that really weren't factors. For example, if we bought a rabbit's foot as a good luck charm and then got a raise at work, we might conclude that the rabbit's foot was the reason why we got the raise. Why we jump to this conclusion is somewhat understandable because we're conditioned to always look for the easiest or most immediate explanation for the cause of an event.

When it comes to our brains determining causation, there are three fallacies in logic that may attempt to trick us into believing a relationship between a cause and an effect exists that really does not. These particular fallacies of causation are quite similar to one another and include the fallacies of post hoc, mere correlation, and oversimplified cause.


Post Hoc - the idea that if an event happens immediately before another separate event that the prior event caused the following event.

Mere Correlation - the idea that if two events happen at the same time that one causes the other.

Oversimplified Cause - the idea that only a single event or reason is the cause for something when there were actually multiple events or reasons.

Post Hoc

The fallacy of post hoc actually comes from the longer Latin phrase, ''post hoc ergo propter hoc,'' which translates to ''after this, therefore because of this.'' This translation is important because it touches on how we, as humans, think. We tend to think in sequences, believing that for every event there is a cause and effect relationship, and we assume that things continue in this way in a chain reaction fashion.

The example we gave previously of buying a rabbit's foot and then getting a raise is an example of the post hoc fallacy. We are tempted to conclude that buying the rabbit's foot somehow caused us to get a raise, which is clearly not true. If it were, my suggestion would be that rabbits start hiding for fear of losing their feet. Another example might include you watching a baseball game and wishing really hard that your favorite player hits a home run while he is up to bat. If he actually does hit a home run, we might be tempted to assume that our wishes were the cause. Obviously, there is no reason to believe that our wishes somehow caused the home run.

Post hoc fallacy

Mere Correlation

We also tend to mistake causation when two or more events happen together. This is called the mere correlation fallacy or sometimes known as the cum hoc fallacy. So to keep things straight with the post hoc fallacy, remember that the word ''post'' means ''after.'' So one event happening after another is different than cum hoc, where they happen together.

A famous example might be that people who tend to eat ice cream when it's hot outside also tend to be the victims of violent crime. This might lead someone to assume that eating ice cream causes violent crime. It's true that there is a correlation between the both events as they both rise when it is hot. However, correlation between two events doesn't predict causation. In this particular example, there is a third factor that causes both events, namely summer. As summer approaches people tend to eat more ice cream and people tend to be outside more, which brings with it increased chances for robberies and assaults.

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