Should you use an apostrophe when you write about “a good night’s sleep”? Yes.
You’ve probably heard a teacher say that an apostrophe signifies ownership. That statement is correct, but it’s only part of the apostrophe story.
Apostrophes signify “of” ideas. Mary’s car means “car of Mary.” Dennis’ dog means “dog of Dennis.” Three weeks’ pay means “pay of three weeks.” And so on.
The apostrophe in “a good night’s sleep” means “sleep of a night.”
Time expressions often use apostrophes. A day’s pay means “pay of a day.” Two weeks’ vacation means “vacation of two weeks.” A moment’s delay means “delay of a moment.”
“Before the s or after the s?” If you take a minute to look at the example, you’ll have the answer: Spell the word (day, days, week, weeks, night, nights, moment, moments, Dennis, Mary) and put the apostrophe after the last letter.
Here are some examples:
a day’s delay
two days’ delay
a week’s pay
two weeks’ pay
a good night’s sleep
two nights’ dreams
a moment’s delay
several moments’ anxiety