Expressions creep into our vocabulary that we come to accept as “normal,” but what is considered “normal” speech in a professional setting is not the same as what is “normal” for a kid hanging out in the schoolyard. In your writing and your speech, take a moment to think about the words you are using. Are you actually saying what you believe you are saying?
“I could care less.”
The usual point people are trying to make when they misuse this expression is that they don’t care. (The correct wording, “I couldn’t care less,” means you care so little that “less than zero” is not caring at all: if you don’t care (at all), then you can’t care “less.”) But if you could care “less,” then what you are actually saying is that you do care; there’s room for you to care “less.”
In some situations, saying “I don’t care” outright would be even ruder than the flip “I couldn’t care less.” Soften your tone, as appropriate, with a reply such as “I don’t have a preference,” if asked for your input, or, “Whatever you decide to do is fine with me,” when informed of someone’s plans.
On the subject of “could” . . .
Don’t use the preposition of as an auxiliary verb in place of have:
“I could of sworn I paid that bill!” X
“I could have sworn I paid that bill!” ✓
“I must of left my hat at the theater.” X
“I must have left my hat at the theater.” ✓
“I should of known he’d turn out to be a loser.” X
“I should have known he’d turn out to be a loser.” ✓
“I might of gone if I’d known she would be there.” X
“I might have gone if I’d known she would be there.” ✓
What about dialogue?
The dialogue you write for a character in a work of fiction must sound natural, but what constitutes “natural” will depend on the character’s age, level of education, personality, and experience, as well as the setting. A writer must carefully tailor the speech of each character, thereby adding a distinctive style to dialogue (or narrative). Grammatical correctness is not the primary consideration; however, a balance must be struck between readability and originality.*
In the case of have/of, consider using the letter a (short for have) instead of the word of when writing dialogue for a character who is hanging out in the schoolyard:
“I woulda finished school but my father kicked me outta** the house when I was fifteen. I had to work to eat.”
“I’da been dead meat if you hadn’t come along when you did.”
Contractions also add informality:
“She’d have told you if you’d asked.” (Instead of “She would have told you if you had asked.”)
“You could’ve called.” (Instead of “You could have called.”)
* There are, of course, exceptions—like Finnegans Wake, or Mammy’s dialect in Gone with the Wind. (Have you read either?)
** Outta can also be spelled “outa” (which would make more sense, as “out” has only one t, but is rarely used). An apostrophe can also be used to shorten of:
It’s out o’ this world!
He’s out o’ luck.
And if you are curious about the Irish surnames that begin with O’ you might enjoy this article.