Q: I’m confused by a passage in your “Sui genitive!” post about when to use a singular noun and when to use a plural in adjectival phrases: “two-dollar word” vs. “Thirty Years’ War.”
A: Here’s the relevant passage from our Aug. 10, 2010, post about adjectival phrases (we’ll set it off in italics).
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.”
What we mean is that adjectival phrases consisting of a number plus a noun (like “thirty-year” and “two-dollar”) are normally formed with a singular noun (“year,” “dollar”).
This is true whether the noun being modified by the adjectival phrase is singular or plural.
Hence expressions like “thirty-year mortgages” and “two-dollar words.” We don’t say “thirty-years mortgages” and “two-dollars words.” The noun that’s part of the adjectival phrase stays singular.
Now for the “however” exception we mention in our earlier post.
Sometimes a phrase like this becomes plural, loses its hyphen, and gains an apostrophe. An example is “six dollars’ worth” (instead of “six-dollar worth”).
Here the phrase is being used in the genitive case. (If the genitive seems possessive, that’s because the possessive is one of its forms.)
The genitive is used in a handful of expressions, many of them involving numbers, that have developed by tradition or convention.
The genitive is used, for instance, when the noun “worth” is modified by a numerical phrase, as in “five cents’ worth” or “three days’ worth” or “two cups’ worth.”
Ask yourself, How much worth? The worth “of five cents” or “of three days” or “of two cups.” The apostrophe signifies that an unspoken “of” is involved here.
The genitive is also used when the noun “experience” is modified with a numerical phrase, as in “20 years’ experience.” How much experience? The experience “of 20 years.” Again, the apostrophe signifies an unspoken “of.”
The “of” (whether present or not) is also characteristic of possessives. Possession is sometimes indicated with an apostrophe and sometimes with “of.” Examples: “the boy’s feet” … “the feet of the boy.”
As we said, one function of the genitive is to denote possession. However, the definition of “possession” is sometimes hazy, as with “the river’s edge” (or “the edge of the river”). This is why “genitive” is a wider term than “possessive” alone.
With genitive phrases, whether they include numbers or not, you can usually picture an imaginary “of,” as in these examples:
“two weeks’ pay” … the pay of two weeks
“six hours’ time” … the time of six hours
“for convenience’ sake” … for the sake of convenience
“three days’ work” … the work of three days
“a summer’s day” … a day of summer
“for old times’ sake” … for the sake of old times
“in harm’s way” … in the way of harm
“at wits’ end” … at the end of one’s wits
These genitive constructions are different from simple adjectival phrases. They have a different kind of relationship with the noun they modify (as we discussed in that blog entry).
A special note about names of wars. The names for historical events are handed down by tradition—sometimes you’ll see a hyphen and sometimes not.
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).
Historical names like these develop through common usage, and not according to grammatical rules.
To sum up, when numbers are used in modifying phrases, MOST of the modifiers will be singular and hyphenated: “Senators serve six-year terms” (note the singular “year”).
But when the phrase isn’t merely adjectival, but functions as a genitive—as if it owns, or possesses, the noun it modifies—then drop the hyphen and use an apostrophe:
“He has six years’ experience in the Senate.” (Imagine it as “the experience OF six years.”)
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