This week I will look at the fallacy of false cause and in particular the post hoc, ergo propter hoc fallacy. These fallacies occur when one conflates the fact that two things occur at the same time or in close succession with the conclusion that one caused the other.
Post Hoc, Ergo Propter Hoc
This neat little clip from the West Wing gives a good example:
Transcript
For those of you with bandwidth issues, here is the transcript from the clip:
LEO
What else?
C.J.
The Ryder Cup team is declining our invitation to come to the White House.
LEO
You’re kidding.
C.J.
Because of the joke.
BARTLET
You’re kidding.
C.J.
I’m not.
[Mrs. Landingham comes in and gives Bartlet his schedule.]
BARTLET
The Ryder Cup team?
C.J.
It’s a group of the best golfers in the country…
BARTLET
I know what the Ryder Cup team is. Thanks Mrs. Landingham.
C.J.
Sir, this may be a good time to talk about your sense of humor.
BARTLET
[looks at his schedule] I’ve got an intelligence briefing, a security briefing, and a 90-minute budget meeting all scheduled for the same 45 minutes. You sure this is a good time to talk about my sense of humor?
C.J.
No.
BARTLET
Me neither.
LEO
What else?
C.J.
It’s just that it’s not the first time it’s happened.
BARTLET
I know.
TOBY
She’s talking about Texas, sir.
BARTLET
I know.
C.J.
U.S.A. Today asks you why you don’t spend more time campaigning inTexas and you say it’s ‘cause you don’t look good in funny hats.
SAM
It was “big hats.”
C.J.
What difference does it make?
BARTLET
It makes a difference.
C.J.
The point is we got whomped in Texas.
JOSH
We got whomped in Texas twice.
C.J.
We got whomped in the primary, and we got whomped in November.
BARTLET
I think I was there.
C.J.
And it was avoidable, sir.
BARTLET
C.J., on your tombstone, it’s gonna read, “Post hoc, ergo propter hoc.”
C.J.
Okay, but none of my visitors are going to be able to understand mytombstone
BARTLET
Twenty-seven lawyers in the room, anybody know “post hoc, ergo propter hoc?” Josh?
JOSH
Uh, uh, post, after, after hoc, ergo, therefore, after hoc, therefore, something else hoc.
BARTLET
Thank you. Next?
JOSH
Uh, if I’d gotten more credit on the 443…
BARTLET
Leo?
LEO
After it, therefore because of it. [Josh, a little weirded out, looks]
BARTLET
After it, therefore because of it. It means one thing follows the other, therefore it was caused by the other, but it’s not always true. In fact, it’s hardly ever true. We did not lose Texas because of the hat joke. Do you know when we lost Texas?
C.J.
When you learned to speak Latin?
BARTLET
Go figure.
Translation
The banter which makes the West Wing such a great program gets in the way here, the main gist is this:
C.J.
The Ryder Cup team is declining our invitation to come to the White House.
Because of the joke.
Sir, this may be a good time to talk about your sense of humor.
It’s just that it’s not the first time it’s happened.
TOBY
She’s talking about Texas, sir.
C.J.
U.S.A. Today asks you why you don’t spend more time campaigning in Texas and you say it’s ‘cause you don’t look good in funny hats.
The point is we got whomped in Texas.
We got whomped in the primary, and we got whomped in November.
And it was avoidable, sir.
BARTLET
C.J., on your tombstone, it’s gonna read, Post hoc, ergo propter hoc – “after it, therefore because of it.”
It means one thing follows the other, therefore it was caused by the other, but it’s not always true. In fact, it’s hardly ever true.
In this video, character C.J. argues that because President Bartlet made a joke about Texan hats prior to two unsuccessful votes in Texas, it follows that the joke was the reason he lost the votes. Bartlet points out that this inference is fallacious because it assumes that if one thing follows another then the first thing caused the second; this assumption is a fallacy of logic. C.J.’s argument committed the post hoc, ergo propter hoc fallacy.
Examples
It is easy to find counter example to the claim that because one thing follows another the former caused the latter. Roosters crow just before the sun rises. It does not follow from that roosters crowing causes the sun to rise.
Despite examples like this illustrating the error of this kind of reasoning, it is not uncommon to hear this kind of fallacy in public policy debates. One example occurred during the New Zealand election a few years ago. The incumbent Labour government ran advertisements which stated “under Labour, the economy has improved”. The advertisement claimed that after the Labour Party got into power the economic situation improved. Its context in a political promo advertisement suggests the information was given to encourage us to conclude that Labour’s policies had improved the economy. Unfortunately this was a fallacy.
Labour’s policies may or may not have improved the economy but the mere fact that the economy improved after they got into power does not show they were the cause. This was made clear when towards the end of Labour’s term an economic recession hit New Zealand. At that time, Labour explained that the recession was not their fault but that it was due to trends in the international market.
Now I am not denying that the recession was caused by international economic trends. Neither am I trying to single out Labour – I suspect the reasoning and propaganda from other political parties fares not much better. The point I am getting at is that one cannot infer that because the economy improved after Labour came to power that Labour caused it in one instance but then when the economy went bad, again after they came to power, that Labour were not the cause of it. This seems to be a case of trying to have your cake and eat it too. In both cases certain economic events happened after Labour got into power. The causal relationship was more complex than the mere fact that a particular political party was now in power. It could have been that both the improvement and the down-turn were due to international trends; it could have been that both were due to Labour’s policies or they both could have been due to something else. In fact, it could have been that one was policy based and the other was based on international trends and so on. The point is, that without other information, one cannot infer cause simply from temporal priority – one simply occurring after the other.
False Cause
Post hoc, ergo propter hoc, is one version of a series of fallacies known as fallacies of “false cause” which mistakes correlation with causation. These fallacies assume that because two events occur together, closely in time, there is a causal relationship between them.
A few years ago, I heard someone arguing against imprisonment as a form of punishment. His argument was that jurisdictions which have high imprisonment rates also have high crime rates. He concluded that this was evidence that the former caused the latter and thus imprisonment was a poor deterrent.
However, as an astute critic pointed out this was clearly fallacious (at least in states where due process exists). It is possible, for example, that the causation goes the other way; the reason the jurisdiction had a high imprisonment rate was that it had a high crime rate – in states where more people commit crimes, more people go to jail for doing so.
The mere fact that two things like this are co-related proves very little; correlation is not causation.
Another more humorous example: a friend of mine once, tongue in cheek, told me that it was a statistical fact that ice cream sales increased every year at the same time crime did. I do not know whether this statistic is correct, but suppose it is. It is easy to speculate as to some reasons why this fact might be the case. In my part of the world, summer falls over the New Year’s period, people are off work, teenagers are out and people around the New Year’s period engage in heavy drinking in certain holiday “hot spots”. This often leads to riots, vandalism and a crime spike for the week around New Year’s. At the same time, the increased heat and increased people out on the streets instead of at work or school increases the demand for ice cream. One can imagine then situations in which both crime increases and ice cream sales rise due to other factors such as the time of the year and the temperature. It would be silly to claim that one caused the other and to propose a ban on ice cream as a serious method of lowering crime. Correlation is not causation.
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