I couldn't care less VS. I could care less

Think about it, most people usually do say "I COULD care less" when in fact they mean they COULDN'T care less. How could there be such a bastardised and widely misspoken but understood phrase? For some reason this conundrum popped into my skull and I decided to research it.

Apparently the phrase, like all good things, is originally British.

I couldn't care less and I could care less, each of which (at least here in America) are used to mean the same thing (which is basically I really don't care), even though their syntax suggests that they should be opposites.

The form I could care less has provoked a vast amount of comment and criticism in the past thirty years or so from nerds and sticklers of syntax abroad. The original expression, of course, was I couldn't care less, meaning "it is impossible for me to have less interest or concern in this matter, since I am already completely indifferent".

I could care less was apparently coined in the US and is found only here. It may have begun to be used in the early 1960s, though it turns up in a written form only in 1966.

Attempts to be logical about I could care less have failed. Taken literally, if one could care less, then one must care at least a little, which is obviously the precise opposite of what is meant. The intent is obviously sarcastic — the speaker is really saying, "As if there was something in the world that I care less about".

However, this doesn't explain how it came about in the first place; how did it go from couldn't to could? Was it misheard and misused and so on and so forth like a game of telephone? Something caused the negative to vanish even while the original form of the expression was still very much in vogue and available for comparison / correction.

There's a close link between the stress pattern of I could care less and the kind that appears in certain sarcastic or self-deprecatory phrases that are associated with the Yiddish heritage and especially New York Jewish speech / slang.

Perhaps the best known is I should be so lucky!, in which the real sense is often "I have no hope of being so lucky", a closely similar stress pattern with the same sarcastic inversion of meaning. There's no evidence to suggest that I could care less came directly from Yiddish, but the similarity is suggestive. There are other American expressions that have a similar sarcastic inversion of apparent sense, such as Tell me about it!, which usually means "Don't tell me about it, because I know all about it already". These may come from similar sources.

So it's actually a very interesting linguistic development. But it is still regarded as slang, and also has some social class stigma attached. And because it is hard to be sarcastic in writing, it loses its force when put on paper and just ends up looking stupid. In such cases, the original form, while still rather colloquial, at least will communicate your meaning — at least to those who really could care less.

Sources: Harper Dictionary of Contemporary Usage, "I Couldn't Care Less" a 1946 book by Anthony Phelps, The Language Instinct and World Wide Words.