top of page

Post Hoc, Ergo Propter Hoc

It is an unfortunate thing that such a common logical fallacy has such an inaccessible name. Few people enjoy reading Latin! But this logical fallacy is not as difficult to understand as it is to read. Let me begin with an illustration.

Imagine an NFL quarterback who doesn't have a great record. He's getting ready for the next big game and realizes that he had forgotten to do laundry that week. He is almost completely out of socks, and the only suitable pair of socks he has are a bright, neon green pair of socks. In spite of their conspicuousness, he figures that he has no other choice and wears them to the game. Unexpectedly, he leads his team on to a great win, beating the other team by three touchdowns! As he reflects on the win, he figures that the socks must be lucky and decides to wear them at every game from that game on.

This is an example of superstition in sports, and that kind of thing is quite common. It's also somewhat silly. Clearly, his team's victory has nothing to do with the socks he wore. The two are a coincidence. But, because he decided to wear the socks before the game, he acts as if wearing the socks caused that victory. This is post hoc, ergo propter hoc.

In English, the term literally means "after this, therefore resulting from it." It assumes that, for events A and B, if B follows from A, then A caused B. In other words, if the relation between A and B is sequential, the fallacy mistakes a sequential relation for a causal relation.

Examples of this fallacy can be seen everywhere in daily life. Superstitions, like the one cited above, are common instances of post hoc, ergo propter hoc. Another very common example is medical. For those who tend to be anxious about their health (as I can be at times), this fallacy is common and at times can be just as silly (though not for the anxious person) as superstitions. "I ate a particular kind of cereal this morning and later had a persistent cough. So, that cereal causes a persistent cough for me. I better not eat it anymore!"

Unfortunately, and more seriously, conspiratorial thinking can also generate examples of post hoc, ergo propter hoc. Let's look at one recent example. After the COVID-19 vaccines were released, reports began emerging of people who were suffering health complications after having received the vaccine. The most common reported complications were myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the outside lining of the heart). But after some complications were reported, people began finding all sorts of other complications. In one instance, I heard someone claim that the vaccine had actually been made to control the population and that people would soon be dying by the millions from complications as a result of the vaccine!

Notice how a logical fallacy is the reason why certain scientific evidence is taken to support a conspiracy theory's claims. There are some complications that can, in rare cases, result from getting the vaccine. But, with hundreds of millions of people having received the vaccine, we should expect that some of those people will, coincidentally, suffer from health issues not long after receiving the vaccine. This doesn't imply that the vaccine caused those health issues. All of them could, for all we know, be coincidental. In other words, establishing a causal relation requires more evidence than a sequential relation. This is the mistake in the reasoning of many that, unfortunately, has led to conspiratorial thinking.

Why care about this fallacy? I care about this fallacy for the same reason that I care about all fallacies: I want you to think well. I want Christians, especially, to think well. We worship a God who is the source of all truth, reason and logic. If we claim to worship Him, and by worshipping Him claim to follow His Son, then it follows that we have a duty to think well. Jesus would never draw a false conclusion from true premises. Of course, we are finite and make mistakes, but we should consider it part of our duty as Christians to think well, insofar as we can. To reason well in an orderly way is to love God with our own minds.

I am grieved when I reason badly and when I see Christians reasoning badly because to reason badly is to fail to love God with our minds as fully as we can. Tragically, conspiratorial and superstitious thinking is rampant among Christians today, and that does not honor God or Christ. I hope that the content of this series helps you to practice intellectual humility in a way that aids your worship of the Lord, realizing that reasoning well is an act of worship that pleases God.

That's it for this post! These posts are intended to very short and easy to read. I want them to a helpful resource for reference and an introductory resource for people who haven't been exposed to these concepts. I hope that the content will be edifying to you. If you have questions or would like to reach out to me to discuss these things, feel free to comment here or to send me an email or message on Facebook. If this blog has been helpful and interesting for you, feel free to subscribe to be notified of any new posts. Finally, if this post would benefit anyone else, please feel free to share it on social media. Thanks for reading!


For the sake of full disclosure, this is the main resource that I will be using for this series. This is an excellent textbook and worth checking into if you want more information on the subject:

Hurley, Patrick J. A Concise Introduction to Logic. Twelfth Edition. Stamford, CT: Cengage Learning, 2015.

Recent Posts

See All


bottom of page