United States.
Part A: Number. A century ago, in American English, this proper noun had “ceased to have any suggestion of plurality about it.” Harry T. Peck, What Is Good English? 3, 16 (1899). That represented a change, though, from just 50 years before, when states’-rights particularism was rampant. Thus, much earlier even than 1850, it was usual to say the United States have, as Alexander Hamilton did in The Federalist No. 15, at 108 (Clinton Rossiter ed., 1961).
Today, however, it’s unidiomatic to suggest plurality in referring to the United States. But some British English writers use the phrase in this way — e.g.: “It has been shown that under the law of some of the United States [read some states in the United States or some American states] there is a legal advantage.” Glanville Williams, The Sanctity of Life and the Criminal Law 183-84 (1957; repr. 1972).
Language-Change Index — “United States” used as a plural: Stage 1.
Part B: Possessive. Like other words that are singular in meaning but formed from a plural, “United States” forms the possessive by adding an apostrophe alone {United States’ interests}.
For information about the Language-Change Index click here.
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Quotation of the Day: “The most convenient test of an idiom is: can it be translated word for word into a foreign language without producing nonsense?” G.L. Brook, Words in Everyday Life 15 (1981).
