Personally speaking, I find the usage of “I could care less” instead of “I couldn’t care less” to be a little annoying. I’d even go further: to my ear it sounds illogical: “hey, if you could care less then you must care a bit!” Much merriment and good-natured joshing ensue, ho, ho, ho. But, to be honest, life’s too short to start a grammar war over it.
I’ve even encountered the theory (I believe it was Steven Pinker who first proposed it) that the speaker of “I could care less” is being sarcastic: “hey, I could care a bit, but, like, it’s so not worth the effort”. But then again, “I couldn’t care less” is also being sarcastic by using emphasis: whatever happened to the simple “I don’t care”? Besides which, it’s used so often in an automatic unthinking manner that it’s a little presumptuous to imagine that every usage is sarcasm (ditto the “negated” version, I suppose).
They are both idioms. They don’t have to really make sense literally: you are conveying the thought through the cliché. People don’t really hear the words, they hear the shape of the saying and get the meaning from that. You cannot fail to miss with colloquial phrases. Everyone knows them. Here’s one: “I’m head over heels in love with you”. You all know this one, it means “I’m bowled over by you”, and maybe you’ve even had it said to you. And yet you’ve never really read it. Look, when I’m standing upright, my head is over my heels. So, I’m in love with everyone I meet as I walk around the mall? Duh. (Brewer’s Dictionary of Phrase and Fable states that the saying used to be “heels over head” which makes a lot more sense. But the idiom changed over the years.)
In essence, it’s part of a problem with how our poor monkey brains deal with negation (or even over-negation) in sentences, especially in conversation. Sometimes it seems there’s just not enough time for the brain to process the complicated grammar, craft a sentence, and get the mouth to say it; or even the other way around: to hear and parse what someone else is saying to you. No one is too intelligent to avoid misinterpreting over-negated sentences. We just cancel out some of the (explicit/implicit) negation and somehow hear what the other was trying to say, even if the sentence literally meant the opposite. Heck, I know de Morgan’s Laws and yet I still have problems writing complex conditional expressions with
not operators. I have to stop and really think about what I’m trying to say.
So, before you all jump over me for condoning “could care less”, maybe you should reread what I wrote.
Orbit, William - Fire and Mercy
(from The Best of Strange Cargos)