What common grammar 'correction' do people make that is actually grammatically incorrect?
The correction of "less" to "fewer" is a classic example of a "rule" that isn't actually a rule. People love to jump in and say "fewer" must be used for anything you can count, like people or cookies, while "less" is only for uncountable things like water or time.
In reality, "less" has been used with countable nouns for over a thousand years. The idea that it's "wrong" was started by a single grammarian in 1770 who simply preferred the sound of "fewer." There is no syntactical reason to forbid "Twelve items or less" at the grocery store, yet people treat it like a major linguistic crime.
what about you?