What's a Double Negative?
This grammar no-no isn't all bad.
I made an embarrassing mistake the other day. I wrote "I can't hardly believe . . ." when I should have written "I can hardly believe . . ."
"Can't hardly" is an example of a double negative—something writing experts say you should avoid—and it also doesn't make much sense. Often double negatives mean the opposite of what you are trying to say.
Occasionally, double negatives are useful when you want to place emphasis on something bad. I recently read a sentence in the New Scientist that referred to less unhealthy cigarettes. "Less unhealthy" is a double negative—"healthier" would be the positive descriptor—but "less unhealthy" keeps the emphasis on cigarettes' dangers.
Other examples of double negatives (and poor word choices) include