According to some of the calendars and appointment books floating around this office, Monday, February 19th, is Presidents’ Day. Others say it’s President’s Day. Still others opt for Presidents Day. Which is it? The bouncing apostrophe bespeaks a certain uncertainty. President’s Day suggests that only one holder of the nation’s supreme magistracy is being commemorated—presumably the first. Presidents’ Day hints at more than one, most likely the Sage of Mount Vernon plus Abraham Lincoln, generally agreed to be the greatest of them all. And Presidents Day, apostropheless, implies a promiscuous celebration of all forty-two—Jefferson but also Pierce, F.D.R. but also Buchanan, Truman but also Harding. To say nothing of the incumbent, of whom, perhaps, the less said the better.
That's the lede of Hendrik Hertzberg's Comment piece in the February 19 and 26 New Yorker. The answer to the trick question in the fourth sentence is "Washington's Birthday." Hertzberg again: "According to Prologue, the magazine of the National Archives, [Presidents Day] was a local department-store promotion that went national when retailers discovered that, mysteriously, generic Presidents clear more inventory than particular ones, even the Father of His Country. Now everybody thinks it’s official, but it’s not."