There are many logical fallacies, and over the last year and a half, I’ve focused on several of them.
While fallacies are typically from the debating sphere and may seem out of place on a blog dedicated to writing, they do appear in writing as well. And not just in social media and blog comments either. They can appear in website and marketing copy, political speeches, opinion pieces, and so on.
Today’s fallacy is post hoc ergo propter hoc.
What is the post hoc ergo propter hoc?
A post hoc ergo propter hoc argument is when the speaker’s conclusion assumes that because one event occurred after another event, the latter must have caused the former.
You’ve probably actually heard an example of a post hoc ergo propter hoc and not even realized that’s what it was.
For example, have you ever heard someone say, “I got a flu shot, yet I still got the flu. The flu shot gives people the flu!”? This conclusion assumes that this is the only cause, ignoring other possible causes, such as already being infected by the flu when you got the vaccination.
This is timely for me. Lethbridge has a supervised consumption site, which is designed to provide medical supervision while people consume drugs. They also often provide drug supplies (such as needles, vein ties, and alcohol swabs). These sites reduce infection transmission rates and can respond almost instantaneously to overdoses, reducing death risk.
In the two years that the SCS has been open, crime has risen. Some people assume that since crime went up after the SCS opened, it must have caused the crime increase. That is a post hoc ergo propter hoc argument. When you delve into the data, however, you find that crime has actually been increasing for at least 5 years, so the SCS can’t be the cause—or at the very least, not the primary cause.
Examples of the non sequitur fallacy
Here are some other examples of the post hoc ergo propter hoc fallacy:
- During the summer, swimming deaths and ice cream consumption both rise, so ice cream consumption must be causing pool drownings.
- As people grow, their feet size increase as their handwriting improves, so foot size must cause good handwriting.
- Every time I wear my Cleveland Browns jersey, the Browns win, so the jersey affects game outcomes.
- A restaurant launches a massive advertising campaign promoting their new menu, and it leads to a huge increase in sales, so the new menu must have created the new business.
- I washed my van and then it rained that night, so my van washing must have caused the rainfall.
In all the above examples, the speaker assumes a causal connection between two events, despite there being other possible explanations for their correlation.
Using post hoc ergo propter hoc is unfair to those you debate, and it’s intellectually lazy for you. Hopefully, these examples explain the importance of focusing on proposing logical arguments.
Which logical fallacy should I cover next? Let me know in the comments below.
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