The Grammarphobia Blog

Sui genitive!

Q: I have a grammar question that’s been bothering me. If we say “the Six-Day War” and “the seven-year itch,” why do we also say “the Hundred Years’ War” and “five years’ experience”? Is there a difference I’m unaware of?

A: Normally, nouns used with numbers to form adjectival phrases are singular, as in “two-inch rain,” “three-year-old boy,” “two-dollar word,” “eight-volume biography,” and “four-star restaurant.”

However, where a plural noun is used by tradition to form such a phrase, it’s generally followed by an apostrophe, as in “the Thirty Years’ War” and “the Hundred Years’ War.”

The plural followed by an apostrophe is also used in phrases like “ten dollars’ worth” or “five years’ experience” or “two days’ time.”  

Apostrophe constructions like these aren’t “possessive” in the sense of ownership; strictly speaking, they’re genitive. 

As we’ve written before on the blog, genitives involve relationships much wider than simple possession or ownership. One such relationship is measurement, as in “two weeks’ pay” or “six hours’ time” or “five years’ experience.”

Other common examples of genitives include “a summer’s day,” “for old times’ sake,” “in harm’s way,” and “at wits’ end.” (We’ve discussed “at wits’ end” on our blog as well, in case you’re interested.) None of these apostrophes indicate possession, strictly speaking. 

Where measurements are concerned, we often have a choice of modifying phrases. Let’s say we’re waiting on the tarmac for our plane to take off.

We can use either a plural noun in the genitive case (“a three hours’ wait”), or a singular noun as part of an ordinary compound adjective (“a three-hour wait”).

Either way, it’s a long wait!

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