You always mean: Couldn't care less
Why: You want to say you care so little already that you couldn't possibly care any less. When the Boston Celtics' Ray Allen said, "God could care less whether I can shoot a jump shot," we know he meant exactly the opposite because 1) God has other things on his mind, and 2) God is a Knicks fan.
You might say: Mano a mano
You might mean: Man-to-man
Why: You don't speak Spanish by adding vowels to the end of English words, as a columnist describing father–teenage son relationships seemed to think when he wrote, "Don't expect long, mano a mano talks." Mano a mano (literally, "hand to hand") originated with bullfighting and usually refers to a knock-down, drag-out direct confrontation.
You might say: Less
You might mean: Fewer
Why: In general, use fewer when you're specifying a number of countable things ("200 words or fewer"); reserve less for a mass ("less than half"). So when you're composing a tweet, do it in 140 characters or fewer, not less.
You never mean: Hone in
You always mean: Home in
Why: Like homing pigeons, we can be single-minded about finding our way to a point: "Scientists are homing in on the causes of cancer." Hone means "to sharpen": "The rookie spent the last three seasons honing his skills in the minor leagues." But it's easy to mishear m's and n's, which is probably what happened to the Virginia senator who said, "We've got to hone in on cost containment." If you're unsure, say "zero in" instead.
You might say: Bring
You might mean: Take
Why: The choice depends on your point of view. Use bring when you want to show motion toward you ("Bring the dog treats over here, please"). Use take to show motion in the opposite direction ("I have to take Rufus to the vet"). The rule gets confusing when the movement has nothing to do with you. In those cases, you can use either verb, depending on the context: "The assistant brought the shot to the vet" (the vet's point of view); "the assistant took the shot to the doctor" (the assistant's).
You might say: Who
You might mean: Whom
Why: It all depends. Do you need a subject or an object? A subject (who) is the actor of the sentence: "Who left the roller skates on the sidewalk?" An object (whom) is the acted-upon: "Whom are you calling?" Parents, hit the Mute button when Dora the Explorer shouts, "Who do we ask for help when we don't know which way to go?"
You almost never mean: Brother-in-laws, runner-ups, hole in ones, etc.
You almost always mean: Brothers-in-law, runners-up, holes in one, etc.
Why: Plurals of these compound nouns are formed by adding an s to the thing there's more than one of (brothers, not laws). Some exceptions: words ending in ful (mouthfuls) and phrases like cul-de-sacs.
You almost never mean: Try and
You almost always mean: Try to
Why: Try and try again, yes, but if you're planning to do something, use the infinitive form: "I'm going to try to run a marathon." Commenting on an online story about breakups, one woman wrote, "A guy I dated used to try and impress me with the choice of books he was reading." It's no surprise that the relationship didn't last.
You almost never mean: Different than
You almost always mean: Different from
Why: This isn't the biggest offense, but if you can easily substitute from for than (My mother's tomato sauce is different from my mother-in-law's), do it. Use than for comparisons: My mother's tomato sauce is better than my mother-in-law's.
You almost never mean: Beg the question
You almost always mean: Raise the question
Why: Correctly used, "begging the question" is like making a circular argument (I don't like you because you're so unlikable). But unless you're a philosophy professor, you shouldn't ever need this phrase. Stick to "raise the question."
You might say: More than
You can also say: Over
Why: The two are interchangeable when the sense is "Over 6,000 hats were sold." We like grammarian Bryan Garner's take on it: "The charge that over is inferior to more than is a baseless crotchet."
You almost never mean: Supposably
You almost always mean: Supposedly
Why: Supposably is, in fact, a word—it means "conceivably"—but not the one you want if you're trying to say "it's assumed," and certainly not the one you want if you're on a first date with an English major or a job interview with an English speaker.
You might say: All of
You probably mean: All
Why: Drop the of whenever you can, as Julia Roberts recently did, correctly: "Every little moment is amazing if you let yourself access it. I learn that all the time from my kids." But you need all of before a pronoun ("all of them") and before a possessive noun ("all of Julia's kids").
You might say: That
You might mean: Which
Why: "The money that is on the table is for you" is different from "the money, which is on the table, is for you." That pinpoints the subject: The money that is on the table is yours; the money in my pocket is mine. Which introduces an aside, a bit of extra information. If you remove "which is on the table," you won't change the meaning: The money is for you (oh, and unless you don't want it, it's on the table). If the clause is necessary to your meaning, use that; if it could safely be omitted, say which.
You never mean: Outside of
You always mean: Outside
Why: These two prepositions weren't meant for each other. Perfectly acceptable: "Wearing a cheese-head hat outside Wisconsin will likely earn you some stares and glares (unless you're surrounded by Green Bay Packers fans, that is)."
You might say: Each other
You might mean: One another
Why: Tradition says that each other should be used with two people or things, and one another with more than two, and careful speakers should follow suit: "The three presenters argued with one another over who should announce the award, but Ann and Barbara gave each other flowers after the ceremony." (By the way, if you need the possessive form of either one when writing that business letter, it's always each other's and one another's; never end with s'.)
8 Confusing Pairs
leery, wary: suspicious
farther: for physical distance
further: for metaphorical distance or time
principal: of your school
compliment: nice thing to say
continual: ongoing but intermittent
continuous: without interruption
stationary: stands still
imply: to suggest a meaning
infer: to draw meaning from something
affect: typically a verb, meaning "to act upon or cause an effect"; as a noun, it's "an emotional response"
effect: typically a noun, meaning "something produced," like a special effect; as a verb, "to bring about," as in "to effect change"