By now, unless you’re the type that refuses to follow the news (not that I blame you, but in that case, why are you reading this newspaper?), you know who “Prisoner X” is. Called “Mr. X” by the Israeli news service Ynet, which originally broke the story of his suicide in a high-security Israeli prison cell in 2010, “Prisoner X” was recently brought again to the world’s attention by an Australian Broadcasting Corporation report that he was in fact a dual Australian-Israeli citizen named Ben Zygier.
All this has now been corroborated by the Israeli authorities, although just what Zygier did to merit his fate remains, at the moment, an enigma.
But the enigma that interests me is of another sort. Why, I found myself wondering, do we use the capital letter “X” to designate nameless people, especially when there is an aura of mystery around them?
At first glance, this usage goes back to at least 1932, when Warner Bros. released the early Technicolor horror movie “Doctor X,” starring Lee Tracy as Dr. Jerry Xavier, a physician who investigates a series of grisly cannibalistic murders. And yet the Doctor X of this movie does have a name, which is where the X of its title comes from. “X” in the sense of “nameless” first turns up, probably under the influence of the Warner Bros. film, in 1944, in the character of The Amazing Mr. X in the British comic book series “The Dandy.”
Subsequently, this meaning of “X” began to spread. There are by now dozens of Mr. X’s in comics, films and video games, plus Ms. X’s, Dr. X’s, Professor X’s and other members of the X family, and “X” long ago entered everyday speech as a way of referring to an unidentified person or (in an expression like “the X factor”) thing.
But the history of “X” as a synonym for “nameless” is far more complicated. It probably starts with the 17th-century French philosopher and mathematician René Descartes, who in his 1637 book “La Géometrie” first systematically used a lower-case “x,” together with “y” and “z,” to signify an unknown quantity in simple algebraic equations. Descartes did this on the model of the ancient Greek geometrician Euclid, who made the Greek letters alpha, beta, gamma, etc., stand for points on lines.
(Who doesn’t remember instructions from his school days like, “Let AB be a line segment bisected at C by DE”?) Since Euclid had chosen the first letters of the Greek alphabet for geometry, Descartes chose the last ones of the Latin alphabet for algebra, and his choice was quickly adopted by other mathematicians.