Logic Me ThisSkepticism

Logic Me This: The Pilot

‘Logic Me This’ is a regular series on Teen Skepchick where we examine various logical fallacies in an attempt to help you think more like a Skeptic.

Fallacies are misconceptions that result from incorrect reasoning. They’re pretty much key to what being a skeptic is all about—the tools skeptics use in their inquiries. We think that they’re important because logical thinking can help us tell where an argument has gone wrong. If we can’t tell what logical fallacies a quack is employing, then we can’t say why they are wrong.

We’re kicking off this week with one of the most common logical fallacies: confusing correlation with causation. The Latin name for this fallacy is Cum Hoc, Ergo Propter Hoc. Translation: With this, therefore because of this. The basic idea is this: Say you are doing a scientific experiment, or even just making an observation in your everyday life, and you notice that two things or events are related (correlated). You then decide that that one of these two events must cause the other.

But this isn’t necessarily true! It might be the case that one causes the other. It could also be the case that what you have called the cause and what you have called the result are the other way around. It could easily be seen that lots of overweight people eat low-fat meals. So we could say that people are overweight because they are eating low-fat meals. But in this case it is easy to see that we have gotten the cause and effect around the wrong way- People are eating the low-fat meals because they are overweight, not the other way around.

Another alternative is that something else altogether might be causing both of these things. You might sell umbrellas for a living, and have a friend who is an ambulance paramedic. You notice that when you have a bumper day and sell a lot of umbrellas that your friend also has a busy day with lots of call-outs. You could say that selling more umbrellas causes people to have more accidents. However, a more likely explanation is that it’s a rainy day- this causes people to buy more umbrellas, and also causes roads to be slippery- thus more accidents!

A third scenario could be plain and simple coincidence. An example of this could be that every time you go to visit your grandma, it rains. Thus, going to visit grandma causes it to rain, right? Not quite. The times you go to visit your grandma are probably only dependent on when you have a weekend free (unless you had a weekend free because the weather was bad, but let’s say for this argument that you had to plan ahead), and weather is so extraordinarily complicated, that you going to visit grandma is very unlikely to be on the list of things that are going to make it rain.

All of the examples I have used so far have been pretty exaggerated and trivial, so you might be wondering why this matters- well, as I said earlier, this fallacy is often used by pseudo-scientists, quack peddlers and people looking to promote their ideologies. Any scientific paper that claims a causal effect should be looked at carefully to see if this causal effect is nothing more than a correlation caused by other things, or a straight-up coincidence. Common alt-med claims sometimes sound like “This patient took my treatment, and now they are cured of their ailment. Thus, my treatment cures that ailment”. Even if the claim is true (often, they’re not), there are many other things that could cause a person to feel better- they might feel better because of actual medicine they are taking, or it could just be the placebo effect.

Other uses of this fallacy are in ideological statements, and people often use them to justify sexist or racist beliefs. For example, someone could say something like: Women earn less than men. Therefore, they are less capable than men, and are really supposed to be homemakers. A logically fallacious statement that is not true and not cool.

So, instead of sidling back into the kitchen when someone says something like that, be skeptical! Be on the lookout for fallacies in your own, and others reasoning.

And with that, I leave you with some xkcd wisdom.

Do you have any other examples? Something in this post not sitting quite right? Do you have any other fallacies you’d like to hear about? Leave us a comment to let us know!

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Lauren is a Maths and Physics student from somewhere in the southern hemisphere. She has an affinity for reality, and you can find her on twitter @lolrj, or Google+.


  1. March 14, 2011 at 9:23 pm —

    One of the better explanations of this logical fallacy that I have read. Well done. 10 of 10.

  2. March 15, 2011 at 8:00 pm —

    Thanks for the feedback, very much appreciated 🙂

  3. May 16, 2011 at 9:21 pm —

    A funny example is the “Pastafarian” tenet that Pirates cause global cooling. To wit, there were more pirates in the 18th century and the world was far cooler. As pirates have vanished the world has steadily warmed!

    Perhaps good old swashbuckling could be used as carbon offsets?

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