Q: I question the use of an apostrophe in “Seven Years’ War.” I assume that “Seven Years” is simply an adjectival phrase modifying the noun “War.” However, your “Sui Genitive!” post supports the apostrophe. I have a book on the subject due for publication next year, and I want the correct punctuation on the cover!
A: In our 2010 post, we say expressions like “a three weeks’ holiday” and “in three weeks’ time” have traditionally taken apostrophes.
If you used the noun phrase “a three-week holiday,” no apostrophe would be used; in that case, “three-week” is simply an adjectival phrase.
But “a three weeks’ holiday” is a different animal. Here “three weeks” is a what’s called a genitive construction—the equivalent of “a holiday OF three weeks.”
Similarly, note the apostrophe in such constructions as “he has five years’ experience,” which is equivalent to “experience OF five years, and “a four days’ journey,” which is equivalent to “a journey OF four days” (alternatively, you could use “a four-day journey”).
We’ll quote the Chicago Manual of Style (16th ed., p. 356) on the use of the apostrophe with genitives:
“Analogous to possessives, and formed like them, are certain expressions based on the old genitive case. The genitive here implies of: in three days’ time; an hour’s delay (or a one-hour delay); six months’ leave of absence (or a six-month leave of absence).”
Garner’s Modern American Usage (3rd ed., p. 647), has the same information. Periods of time and statements of worth are expressed with apostrophes. Garner’s gives these examples: “30 days’ notice (i.e., notice of 30 days), three days’ time, 20 dollars’ worth, and several years’ experience.”
Getting back to your question, “Seven Years’ War” generally takes an apostrophe for the same reason, though it’s sometimes seen without one. Ditto “Hundred Years’ War” and “Thirty Years’ War.”
It would be grammatically correct, of course, to refer to the three conflicts as the “Seven-Year War,” the “Hundred-Year War,” and the “Thirty-Year War,” but those aren’t their traditional names.
However, the 1967 Arab-Israeli War is often referred to as the “Six-Day War,” using an adjectival rather than a genitive construction.
In a 2013 post on our blog, we describe the difference between an adjectival phrase like “two-dollar word” and a genitive phrase like “Thirty Years’ War.”
As we note, “adjectival phrases consisting of a number plus a noun (like “thirty-year” and “two-dollar”) are normally formed with a singular noun (“year,” “dollar”).
In a genitive version of such a construction, the phrase becomes plural, loses its hyphen, and gains an apostrophe.
Our 2013 post includes a note about historical names, including the names of wars, which “develop through common usage, and not according to grammatical rules.”
“That accounts for why we see both ‘the Thirty Years’ War’ (a genitive usage for ‘a war of thirty years’), and ‘the Six-Day War’ (a simple adjectival phrase),” we write.
If you need a big gun as your authority, the Oxford English Dictionary defines the subject of your book this way: “Seven Years’ War, the third Silesian war (1756–1763), in which Austria, France, Russia, Saxony, and Sweden were allied against Frederick II of Prussia.”
The OED also has this citation, from Thomas Carlyle’s The French Revolution, an 1837 book in which the phrase “seven years” is used in the genitive case (though Carlyle uses a hyphen): “In that seven-years’ sleep of his, so much has changed.”