Recently my wife was talking about something that didn’t strike her as important. “I could’ve cared less,” she said, then corrected herself: “I couldn’t have cared less.” If you stop to think about it, the latter is the literally correct expression. If you don’t care about something your level of caring is already at a minimum, so it would not be possible to care less.1 But really both are correct. Responding to the former with, “I think you mean you could not have cared less” would go beyond obnoxious into nonsensical.
“I could’ve cared less” is one of those prescriptively incorrect expressions that is nevertheless the way people actually talk. Linguists have many of examples of these supposed solecisms at their fingertips–flammable/inflammable, can/may, “That is a rule up with which I will not put”–and delight in explaining why they are not ungrammatical. The “error” when you say “Can I use the restroom?” when you “mean” “May I use the restroom?” is actually a demonstration of your linguistic competence. Part of being a native English speaker lies in possessing three pieces of knowledge: 1) that there is a subtle difference in the meaning of “can” and “may” that hinges on the latter being a request 2) outside deontically ambiguous contexts this distinction collapses and “can” can (may?) be used everywhere 3) nevertheless there is a convention of correcting someone else’s use of “can” in a strictly-speaking “may” situation, usually as a way of making fun of the sort of person who would do such a thing.
Could-have/couldn’t-have flounders at step (1). There isn’t a well-understood distinction between the two phrases that native speakers choose to ignore because it’s a difficult phrase to understand. There is a subtle three-way interaction between the irrealis of “could”, the negation of “n’t”, and the relational semantics of “less”–and that’s before you throw “have” into the auxiliary verb pileup. The aspiring martinet must be willing to solve a logic puzzle before being able to get on someone’s case about their supposedly incorrect usage. In its focus on the details of negation, could-have/couldn’t-have resembles the prescriptive criticism of negative concord in English–e.g. “If you say ‘I ain’t got no money’ doesn’t that really mean you have some money?”2 But there’s a difference in that English negative concord is highly stigmatized, whereas could-have/couldn’t-have is mostly overlooked.3
My wife didn’t even say “couldn’t have cared less”. In fluid speech it ran together, sounding more like “couldn’t’ve have cared less”. You have to be listening closely to even hear the distinction. So given all this may I now propose a new English word: couldda. It can appear in any context that admits “could have/couldn’t have” and means the same thing, except it also signals to the listener “I am aware of the subtle logical distinction that may arise at this point and emphatically don’t care because we both know what I mean.”
Question: does this word already exist?
1 The former works if you’re being sarcastic–“I could have cared less (…but it’s not likely)”–but this requires an extra twist of prosody.
2 In both cases the smug prescriptivist ignores the fact that it is English being spoken, not propositional calculus. If upon being asked whether I may dump of pot of hot coffee into his lap he responds “No, no, no, no!” I do not think “Aha!–you said ‘no’ four times, and -1 raised to an even power equals +1” and then proceed to scald him.
3 By the way, my wife disagrees with this judgement and thinks that “could care less” is just plain wrong.