Logical fallacy of the day: Non causa pro causa

FROM JASON’S PILE O’ANNOYANCE — “We spent $23 million on an effort to control gun crime, and we’ve seen shooting deaths decrease by three percent this year,” says a local politician.

The problem is that there are no concrete facts tying the drop in violence to the crime-control program. There’s a fundamental disconnect between what did happen and what the people in charge want me to think happened.


What if there were fewer fatal shootings because it was colder than normal, and criminals didn’t want to go outside? What if there were far more (criminal) gun-related injuries — which was the case where I live — but fewer deaths?

What if there were fewer gang shootings because the criminals became more organized? That’s certainly not an indication that the $23 million program worked.

This rant isn’t about gun crime, though. It’s about how politicians (and other stupid or dishonest people) use two types of fallacies: cum hoc ergo propter hoc and post hoc ergo propter hoc.

Both are Latin, and are subsets of the non causa pro causa fallacy — which as you could guess from the similarity to our word “cause” means roughly, “Dude, you totally haven’t shown me there’s a link between these two things.”

Cum hoc ergo propter hoc, or “they happened at the same time, so they’re linked,” is used in all kinds of fun but fallacious forum arguments. I know I’m guilty of doing this, too.

“iTunes is doing good business and CDs are failing, so online sales are killing CD sales.” I don’t have any solid facts to tie the two together. It’s just an assumption.

Here’s one that Jack Thompson would like ignorant, easily-swayed alarmists to believe:”Vidjagames are getting more violent and there are more school shootings, so kids playing the vidjagames are being trained to be more violent.”

(Editorial aside: If you don’t know what the vidjagames are, how did you get on my Internets? I suggest you seek counseling from the Fast Karate For the Gentleman podcast.)

Post hoc ergo propter hoc, or “this one thing happened and this other thing was the result” can be tricky. Sometimes something is the cause of an effect. The problem is when we forget to do due diligence and tie them together.

The textbook example: “I didn’t use deoderant, and it rained. Therefore, every time I don’t use deoderant, it will rain.”

The geek example: Well, we geeks are too smart for that, aren’t we? Science be praised.


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