expressions - Which is correct: "could care less" or "couldn't care less"?

What's the deal with the phrase "could care less"?

Whilst growing up, I've always known people (parents etc) to use the phrase "couldn't care less", but I've also come across people who use the phrase "could care less" to mean the same thing (that is, "I do not care at all about that").

To me "couldn't care less" seems a lot more logical. If I couldn't care less about something, that implies I do not care about it at all. In contrast to this, to my mind the phrase "could care less" seems to indicate "I do care about this to some degree at least", but that's definitely not the meaning intended.

What's going on here? Is my (logical) analysis correct or in error?

Answer

I've heard it said that "could care less" is meant to be ironic, but I think this is just justification for the bastardisation of an English phrase.

Here we go (from World Wide Words):

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. 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.