The “pornography causes homosexuality” news story that has been making the rounds today is the most delightful example of a classical logical fallacy that I’ve seen in some time, and I expect to call upon it for all discussions of said logical fallacy going forward.

If you haven’t seen the story yet, Senator Tom Colburn’s chief of staff has been claiming that watching any pornography at all, including straight pornography, causes homosexuality:

“Pornography is a blight,” Schwartz told an audience in a crowded room of the Omni Shoreham hotel. “It is a disaster. It is one of those silent diseases in our society that we haven’t been able to overcome very well. Now, I may be getting politically incorrect here. And it’s been a few years, but not that many, since I was closely associated with pre-adolescent boys, boys around 10 years of age. But it is my observation that boys of that age have less tolerance for homosexuality than just about any other class of people. They speak badly about homosexuality. And that’s because they don’t want to be that way. They don’t want to fall into it.”

The argument, as I understand it, is as follows: 10-year-old boys abhor homosexuality, and they do not watch porn. When they grow up and watch porn, they have laxer morals and are thus more open to homosexuality.

This, as any first-year logic student can tell you, is an example of false cause, or cum hoc, ergo propter hoc (the tasteless cross-language puns write themselves, don’t they? (1)), the mistaken notion that because two things are correlated, there is necessarily a causal relationship between them. There is of course an excellent XKCD on this particular fallacy(2).

Generally speaking, there is a third, unmentioned factor that is responsible for both things, in this case puberty.

But wow did this story give me a little bit of logical fallacy glee today. Oh, my tendency to pay more attention to the form of arguments than the content. Someday it will do me in.

1. Purile jokes aside, cum hoc ergo propter hoc means “with this, therefor because of this” and is closely related to the fallacy post hoc ergo propter hoc, or “after this, therefor because of this.”
2. There is a also a correlation between posts where I use the “snide logician” tag and posts where I reference XKCD. Make of that what you will, as long as you don’t assume a causal relationship.

I believed him at the time, of course. But that was before he stole my “every subject is ultimately reducible to mathematics” game!

ETA: My alt text, “Off the panel on the right, there’s a logician wondering why the mathematician is still bothering to prove things in the object language.” doesn’t seem to be hovering over the image for me. It’s supported, though, by this guy