Andy L and Exapno - I could disagree more, but not much more. 
These idioms aren’t like “a coon’s age” or “a month of Sundays”. The original and still more common version says in plain English but in slightly different words what it means: I don’t care. The newer and less common version actually seems to mean the opposite of that, while it seems to be intended to mean the same thing. Because the two phrases co-exist, the “couldn’t” version seems clearly to be preferable.
One wonders if the Dalai Lama could care less about world peace.
My first inclination is to say, “probably not.” He just seems to be wired that way.
This isn’t a matter of opinion. The recorded actual usage by actual people is a fact and the only thing that counts is facts. I’ve given an explanation of why it’s a fact.
You’re free not to use the idiom. I’ve defended many usages I don’t personally use. That I don’t like them doesn’t make their use by others wrong; it’s just a matter of personal style. Criticizing an idiom makes as much sense as criticizing someone else’s dialect. BYW, people can and do change the pronunciation of words depending on setting and context and people can and do use both “I could care less” and “I couldn’t care less” depending on setting and context. One is only preferable in context at the user’s discretion. Which makes it exactly like every other single word and phrase in the language.
Do you have any evidence for this claim—i.e. that the first people to use the phrase “I could care less” did so out of sarcasm rather than out of ignorance and carelessness?
I prefer “couldn’t” myself, but then I prefer “eat your cake and have it, too” rather than the more confusing “have your cake and eat it, too” - but for whatever reason, the latter has taken over from the former, and a native speaker of English knows what it means (see ngram here: Google Ngram Viewer: your cake and eat it,your cake and have it ).
Why do people assume that this is an ignorant usage? It is development of an earlier phrase, with layers of subtlety that do not exist in that phrase; even though it is rarely used in the UK, I respect it as an idiom and do not assume it is inferior in any way.
This argument could also apply to ‘Tell me about it’ and ‘I should be so lucky’, both of which are sarcastic expressions of the opposite sense to the phrase concerned.
Because plainly, on it’s face, it is an ignorant usage. It literally says the opposite of the meaning it is trying to convey. Furthermore, the original is a double negative type of sentence that trips up a lot of people, so it is easy to imagine that some people started using it wrong, especially given the low level of attention most people give to the literal meanings of idioms.
One could argue that it came about in a different way, but the simplest interpretation of the data is “people dun goofed”.
This alternative hypothesis, that some group of people intentionally changed the phrasing to add some additional layer of subtlety or whatever is possible, but I personally find the “people started saying it wrong out of carelessness, and then later made up the ‘layers of subtlety’ interpretation to avoid seeming foolish when this was pointed out to them” hypothesis to be much more parsimonious with what we already know about human nature.
Then “head over heels” is an ignorant usage but that’s irrelevant. The data also clearly shows that “I could care less” is considered semantically equivalent to “I couldn’t care less” by the english-speaking public, regardless of how pedantically one tries to parse the clause. Linguistically, the matter is settled.
The evidence is indirect, pulled from similar phrases and terms that have reversed literal meaning like those eburacum45 mentioned.
Look at this World Wide Words article from 2001 on the idiom, which may be where he got his examples from.
Here’s an article from Slate that makes all the same points. So does Ben Zimmer when he replaced William Safire’s language column at the Times.
This is so well known, and so often discussed, that it’s irritating to have to bring it up anew each and every time. It’s like the ridiculously snobbery about the use of hopefully, when that parallels dozens of other terms in the language. If you’re going to dump on certain words or phrases, at least take the time to find out if you’re missing a million similar evolutions of language so you don’t look quite as foolish when you get on your high horse.
It certainly is, but when people look at “head over heels”, they say “oh well, it’s just weird, but idioms don’t have to make sense”.
When people loot at, “I could care less”, instead of just saying that a goodly fraction seem to say, “oh no, it actually does make sense if you apply a number of contortions to its plain meaning/assume the speaker is being sarcastic/look for ‘shades of meaning’/&c”.
They wouldn’t if another group of people would shut the fuck up about “hurr durr, you actually mean you do care!”
Pinker says;
Thanks for the link (which also includes the note that “The form I could care less has provoked a vast amount of comment and criticism in the past thirty years or so. Few people have had a kind word for it, and many have been vehemently opposed to it”; so that those of us who are bothered by it at least have company.)
I find the argument you quoted somewhat, but not completely, persuasive. My gut feeling—which I fully admit could be wrong—is along the lines of leahcim’s. To me it sounds more like malapropism than deliberate sarcasm. (In this judgment I may applying a variation of Hanlon’s Razor.)
Truthfully, I don’t find Pinker’s argument all that convincing.
Me neither, and I’m a big fan of his. I don’t hear different stresses or melodies when people say “I could care less” vs. “I couldn’t care less”. The people I hear say it basically the same.
Furthermore, this is how you say, “I don’t care” using a sarcastic tone of voice:
Phrases that are meant ab initio to be sarcastic are overtly sarcastic. This subtle sarcasm we are supposed to read into “I could care less” seems inconsistent with how sarcasm is normally used.
I like and use both. “I could care less” has the advantage of being a malapropism, sarcastic and ironic all at the same time.
“I could care less, but that would require a change in my level of effort.”
A lot of the usage is by people who are repeating what they’ve thought they heard someone else say to diminish something, but they aren’t really thinking. It’s all in the tone.
They may be semantically equivalent, but “I could care less” has a “this is how stupid people talk” vibe to it.
It’s a lot like how “Where’s the washroom?” and “Where’s the shitter?” are semantically equivalent, but the latter option makes the speaker seem uncouth.
It’s much the same as arguing about the modern usage of “literally”, or “try and do x” vs “try to do x.” There is the correct linguistic way to look at it, and then there is the way people talk and are understood.
Personally, I hate “tray and”, but “literally” used as an intensifier doesn’t bug me at all.