A User's Guide
A much-revised and expanded version of this on-line guide, with hundreds of added examples.
Many words and phrases rarely add anything to a sentence. Avoid these whenever you can. A very short list of some of these offenders: Quite, very, extremely, as it were, moreover, it can be seen that, it has been indicated that, basically, essentially, totally, completely, therefore, it should be remembered that, it should be noted that, thus, it is imperative that, at the present moment in time. These are fine in their place, but they often slither into your writing with the sinister purpose of tempting you into the sin of padding your sentences. See Economy.
See That versus Which.
You should usually use who (and its related forms, whose and whom) only to refer to people, with that or which only for non-human things: “a woman who lived nearby” (not that or which); “a concert that set attendance records” (not who).
The only time it's advisable to use who-forms with non-human things is in the whose construction: “the cars that were built by Ford,” but “the cars whose tires were made by Firestone.” That saves you from the very inelegant construction “the cars, the tires of which were made by Firestone.” Even there, though, it's still a little clumsy; if you can reword it to avoid referring to a thing as who, consider doing it. [Entry added 12 July 2005.]
While it's possible to memorize a rule for distinguishing who from whom, it's easier to trust your ear. A simple test to see which is proper is to replace who/whom with he/him. If he sounds right, use who; if him is right, use whom. For example: since he did it and not him did it, use who did it; since we give something to him and not to he, use to whom. It gets messy only when the preposition is separated from the who: Who/whom did you give it to? Rearrange the words in your head: “To whom did you give it?” See Preposition at the End and Hypercorrection.
A confusing pair, like its and it's. Whose means “of whom” or “belonging to whom”; who's is a contraction of “who is” or “who has.” [Entry added 5 Jan. 2005.]
Ad hoc words like salarywise and timewise, meaning regarding salaries or time, are best avoided. Strunk and White put it well: “The sober writer will abstain from the use of this wild additive.”