FWIW Professional Linguists think it's perfectly fine to say "I could care less" and that people who peeve about it are just pointless peevers who don't understand how language works.

That's not the point: "I could care less" is grammatically correct, but the meaning is not what was intended. If I had a cup and wanted to tell you there's no more beer in the cup, I wouldn't say "there's beer in the cup", even though the sentence "there's beer in the cup" would be accepted by professional linguists.

> That's not the point: "I could care less" is grammatically correct, but the meaning is not what was intended.

The intended meaning is obvious. There's plenty of colloquial phrases which say one thing but mean another: "I could murder him", for example, doesn't literally mean that. That is how language works.

And, if you saying "there's beer in the cup" was understood by everyone as meaning "there's no more beer in the cup", professional linguists and dictionaries would be A-OK with that interpretation.

By analogy to vectors though, 'I could murder him' is directionally correct but magnitudinally wrong. Whereas 'I could care less' (as used) is directionally wrong - no you couldn't, your point is how little/not at all you care, so stop talking about the existence of an amount that you do care!

> And, if you saying "there's beer in the cup" was understood by everyone as meaning "there's no more beer in the cup", professional linguists and dictionaries would be A-OK with that interpretation.

The fact that "I could care less" is now clearly understood is not intentional. It's an adaptation to a mistake. It's similar to how people say "irregardless", which is clearly an error. It's unambiguous, and everyone knows what you mean. It's still a mistake, and using "regardless" is strictly better.

> is not intentional. It's an adaptation to a mistake.

Yes, that's what language is. Will you be complaining about "apron" as an adaptation to a mistake?

https://www.quickanddirtytips.com/education/grammar/how-a-na...

> It's similar to how people say "irregardless", which is clearly an error.

It's an error that's been being made since 1795, though, and people have been understanding it which pretty much qualifies it as being incorporated into the language.

(I should note that I am strongly descriptivist and think that prescriptivists are silly people.)

> using "regardless" is strictly better.

I think "regardless" is better, yes, because it's a lot easier to say but that's just my opinion, not a Gilt Edged Rule Of English.

that's kind of a stretch; I would imagine "I couldn't care less" is vastly preferred, and the people that use "I could care less" are most likely doing so out of ignorance and not an intent to convey the subtle "theoretical possibility"