X: the Unknown

by Jeff Oaks

In mathematics, ‘x’ is commonly used as the name for an independent variable or unknown value. While it is widely believed[by whom?] that the usage of ‘x’ to represent an independent or unknown variable can be traced back to the Arabic word šay’ شيء = “thing”, there are no sources to support this claim. Modern tradition of using ‘x’ to represent unknowns was started by René Descartes in his La geometrie (1637).

As a result of its use in algebra, X is often used to represent unknowns in other circumstances (e.g. Person X, Place X, etc.;

See also Malcolm X).

X-rays are so called because their discoverer did not know what they were.

X has been used as a namesake for a generation of humans: Generation X, commonly abbreviated to Gen X. It is the generation born after the baby boom ended, ranging from 1961 to 1981.

Here I am again. I thought I was the end of the boom, but I’m the beginning of the Unknown. Another thing I didn’t realize about myself.

X is commonly used as a generic mark (selecting an item on a form, indicating a location on a map, etc.).

A typographic approximation of the multiplication sign ‘×’ (especially, lowercase Roman “x”). Note that in any font the glyph of “x” is not exactly the same as one of the multiplication sign.

The common custom of placing X’s on envelopes, notes and at the bottom of letters to mean kisses dates back to the Middle Ages, when a Christian cross was drawn on documents or letters to mean sincerity, faith, and honesty.

Usually in art or fashion, the use of X indicates a collaboration with two or more artists.
The application extends to any other kinds of collaboration outside the art world.

X is used by the illiterate in lieu of a signature and indicates a signature line on forms.

In cartoons, a dead character’s eyes are often drawn as Xs.

X is also used for referring to ‘the end of conversation’.

(A collage from Wikipedia)