They vs. he or she
Wrong: I couldn’t tell who the thief was in the dark. They sped off in a hurry.
Right: I couldn’t tell who it was in the dark. The thief sped off in a hurry.
It can be awkward to say “he or she” when the gender of the person referenced is unknown, but it is never correct to refer to one person as they, however tempting. If you must say “he or she” several times in succession, look for other ways to write the sentences. Instead of: “He or she must be apprehended immediately!” try something like: “The (culprit/killer/kidnapper/suspect) must be apprehended immediately!” (In dialog, of course, the speaker can be allowed grammatical indiscretions; but you should be more precise in narrative.)
Fewer vs. less
Wrong: There are less than five hours left until the deadline.
Right: There are fewer than five hours left until the deadline.
Use fewer anytime you can count items. (“This jug contains five fewer gallons of water than that one.”) Use less whenever you can’t count items. (“There is less water in the
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