Apostrophe or no apostrophe? I was editing an article last week when the phrase “nine months pregnant” came up. For some reason, although I knew it was correct, I got stuck on it and stared at it and began to doubt myself. It’s definitely right… I think it’s right… Isn’t it? The phrase “two weeks’ notice” got me all turned around years ago when the movie makers neglected to use an apostrophe in their movie title, and I knew it was incorrect. (I allude to this in my general grammar tip in Writing Tip #26). And if “two weeks’ notice” demands the use of an apostrophe, why doesn’t “nine months pregnant”?
The trick I always use to find out if an apostrophe is needed is to reduce the phrase to its singular form:
She was one month pregnant. No apostrophe.
She gave one week’s notice. Apostrophe.
But I had forgotten the reasoning behind the rule. I did a quick search and found The Guardian, which sums it up this way:
Use apostrophes in phrases such as two days’ time, 12 years’ imprisonment and six weeks’ holiday, where the time period (two days) modifies a noun (time), but not in nine months pregnant or three weeks old, where the time period is adverbial (modifying an adjective such as pregnant or old) – if in doubt, test with a singular such as one day’s time, one month pregnant. (Hey, that’s what I do!)
So if the time period modifies a noun, use an apostrophe. When the time period is adverbial, don’t.
The things that keep me up at night…