How can this be?

While doing some light cleaning around the house this weekend, I noticed that my vacuum cleaner wasn’t the best. I bought it on the cheap, and it doesn’t always pick up dirt and paper shreds and whatnot from my new carpet.

And I thought, “my vacuum cleaner sucks.”

And I laughed.

Because sucking is pretty much what a vacuum cleaner is supposed to do.

I spent a few minutes working on how someone could express that their cleaning instrument wasn’t very good at what it was designed to do, and it made me laugh.

“My vacuum cleaner sucks” and “my vacuum cleaner doesn’t suck” have both the same meaning, and the opposite meaning. At the same time.

I thought of “flammable” and “inflammable” and how, even though the prefix “in-” usually reverses the meaning of the word to which it is affixed, in this one case, it does not. But it’s not entirely the same because the two words just seem like they should mean the opposite. They don’t.

Not like the “vacuum/suck” conundrum.

I wonder if the Language Log folk have ever talked about this?