We used to have two holidays in February: Lincoln’s Birthday and Washington’s Birthday. Now, we have three, though most of us usually get only one of them off: Lincoln’s Birthday, Washington’s Birthday and “Presidents Day.” Er, “President’s Day.” Um, “Presidents’ Day.”

This is going to be fun.

News organizations have used all three presidential iterations for the holiday on the third Monday in February, in surprisingly close proportions. That migrating or missing apostrophe is emblematic of a larger issue in language today—forgetting how to punctuate possessives.

Under ordinary circumstances, forming a possessive is pretty simple: Add “’s” unless the possessor is already plural, in which case add only the apostrophe. The holiday under discussion replaced Lincoln’s Birthday and Washington’s Birthday in many places, so it celebrates more than one president. Thus, it’s “Presidents’ Day.”

Of course, Associated Press style isn’t quite as straightforward as this—it has varying rules for when to use apostrophes with nouns plural in form, singular in meaning; nouns the same in singular and plural; singular nouns not ending in s; singular common nouns ending in s; singular proper names ending in s; special expressions; compound words; joint possession, individual possession; descriptive phrases; descriptive names; quasi possessives; double possessive; and inanimate objects. And that’s not even taking into account that personal possessive pronouns––his, hers, etc.—don’t have apostrophes at all. Perhaps having to understand all those nuances of apostrophiana is what led to the rampant misuse of the possessive apostrophe and, by extension, the contraction apostrophe (as in “its” vs. “it’s”).

Would that it were as easy as that.

The Associated Press Stylebook calls for “Presidents Day,” where “Presidents” isn’t possessive at all, but a descriptive, meaning acting as an adjective. But most dictionaries, including Webster’s New World, the official dictionary of the AP, call for “Presidents’ Day.”

Some states observe Lincoln’s Birthday and “Presidents’ Day”; others have just “Presidents’ Day” (or “Presidents Day”). But as far as the federal government is concerned, “Presidents’ Day” (or “Presidents Day”) doesn’t exist: The third Monday in February is officially designated as Washington’s Birthday. So while calling it “President’s Day” is accurate in a federal, Talmudic way—because it celebrates just one president—it’s wrong. That Washington’s Birthday can never fall on Washington’s actual birthday, Feb. 22 (the third Monday has to fall between the 15th and 21st) seems of no moment to the Feds.

As for where the apostrophe belongs, well, if you follow AP style, forget about it.

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.