• 4-minute read
• 3rd January 2021

How to Avoid the Post Hoc Ergo Propter Hoc Fallacy

Post hoc ergo propter hoc is the Latin name of a common fallacy (i.e. a bad argument) in academic writing. Also known as ‘assuming the cause’, it arises when we get confused about what causes something. For more on what this fallacy involves and how to avoid it in your writing, read on below.

What Is the Post Hoc Ergo Proctor Hoc Fallacy?

Post hoc ergo proctor hoc translates as ‘after this, therefore because of this’. In other words, this fallacy is the mistake of assuming that the order of events implies causation. We can set it out in abstract form as follows:

X occurred before Y, so X must have caused Y.

This is also known as the post hoc fallacy or ‘assuming the cause’.

A similar error is assuming that correlation implies causation, where a pattern of coincidence is taken to show that there must be a causal connection between two phenomena. But here we’re focused on the order of events.

Let’s take a look at some examples of this fallacy in action.

Examples of Post Hoc Ergo Proctor Hoc

This fallacy always begins with an observation of two events occurring in sequence. The mistake is then assuming that the first event caused the second. For instance:

Levels of petty crime went down after the town council raised taxes. This shows that raising taxes is an effective way of reducing crime.

Here, we see that two events occurred in sequence, so we might jump to the conclusion that the first (raising taxes) caused the second (reduced crime). But there is nothing in the statement above that establishes a connection between tax and crime (we don’t even know how the taxes raised were spent). And many other factors may affect crime levels, from policing policy to unemployment levels.

As such, we cannot assume the crime level went down purely because the taxes went up! Unless we know how the two are connected, we can’t draw any conclusions. If we do, we end up fallaciously ‘assuming the cause’.

Most superstitions are based on some form of the post hoc fallacy, too. Take the belief that breaking a mirror leads to bad luck, for instance:

I broke a mirror yesterday, and I’ve been unlucky all day today.

In reality, any bad luck you experience after breaking a mirror is mere coincidence, since there is no causal relationship between mirrors and luck! But if someone breaks a mirror and then notices other things are going wrong afterwards, they might assume that the breakage caused the subsequent bad luck.

The error here lies in imagining a causal relationship where there isn’t one.

Is It Always Wrong to Assume a Cause?

So, is it always wrong to assume a causal relationship between successive events? Not entirely! Causes do precede their effects. Thus, observing that one thing happens before another thing may be reason enough to investigate it further.

However, in an academic context, you need more than just an observation of one thing happening after another to claim a causal relationship. You also need to show that X causing Y is the best explanation available based on the evidence.

How you do this will depend on what you are studying. A sociologist, for instance, might look at statistical data to establish a pattern of cause and effect between different social phenomena (e.g. taxes and crime rates). And in the hard sciences, it might involve conducting an experiment that controls for different variables, allowing you to focus on proving (or disproving) a relationship of cause and effect.

In all cases, though, observing that one thing happens after another should only ever be a jumping off point for investigation. If you simply assume that one event causes another based on their sequence, you’ll be in fallacy territory!

How to Avoid the Fallacy

As noted above, the key to avoiding the post hoc ergo propter hoc fallacy in your work is to base your arguments on evidence as much as possible.

Noticing that one event precedes another event may raise questions, but you need to look at how the two events are related – and whether other factors may be involved or offer a better explanation – to establish a causal connection.

It also helps if you have your writing proofread, since this ensures you can express your ideas clearly. To give our academic proofreading services a try for free, upload a 500-word document today and find out how it works.