Finding X: Why the letter is used for all things unknown

While the letter A also has a similar purpose at times, its position at the beginning of the alphabet could explain why it is the first to be picked when looking for an example. What about X, the 24th letter, falling third to last?

Where the letter X might have come from

According to Dictionary.com, X originally derives from a Phoenician letter, Phonecian being a language spoken in cities bordering the Mediterranean Sea in ancient times. It denoted a hard S sound and the Greeks borrowed this letter called ‘Samekh’ around 900 BC and named it ‘Chi’.

This was used to simplify “the digraph (‘a pair of letters representing a single speech sound’) /ks/, which is used most prominently throughout the western regions of Greece,” it adds.

The Romans later adopted the X sound from the Chalcidian alphabet, a variation of the Greek alphabet. They borrowed the Chi symbol, consisting of two diagonally crossed strokes, to denote the letter X and to identify the Roman numeral X or the number 10, it says.

It is this Greek connection which is also why Christmas is known as X-mas. The website says: “It was first used in the mid-1500s. X represents the Greek letter chi, the initial letter in the word Χριστός (Chrīstos). And what does Χριστός mean? “(Jesus) Christ.” X has been an acceptable representation of the word Christ for hundreds of years.”

The letter’s range of meanings is exemplified in its uses – from sacredness to the explicit. In 1968, the Motion Picture Association of America (MPAA) introduce the X-rating to classify movies depicting adult-only content, usually having explicit language and sexual activity. The choice of the X had to do with the first syllable of the word ‘ex’plicit or the symbolic use for a cross, implying a restriction. Soon, the adult film industry embraced the X-rating, with producers using XXX to market a film.

‘X’ for the unknown

And what is to be said of its role as a mathematics component? Peter Schumer, Professor of Mathematics and Natural Philosophy at Middlebury College, USA, wrote in The Conversation that one theory looks at how Mathematics as a subject developed across various cultures.

“The theory contends that the Arabic word used for the quantity being sought was al-shayun, meaning “something,” which was shortened to the symbol for its first “sh” sound. When Spanish scholars translated the Arabic mathematical treatises, they lacked a letter for the “sh” sound and instead chose the “k” sound. They represented this sound by the Greek letter χ, which later became the Latin x,” he wrote.

But he added that x was not the only representative of an unknown quantity, though it later became extremely popular. Schumer put forward the theory that French mathematician and philosopher René Descartes was behind the modern use of x and wrote: “In an appendix to his major work “Discourse” in the 17th century, Descartes introduced a version of analytic geometry – in which algebra is used to solve geometric problems. For unspecified constants he chose the first few letters of the alphabet, and for variables he chose the last letters in reverse order.”

The simplicity and politics associated with an X

In the book Alphabetical: How Every Letter Tells a Story, British writer Michael Rosen also attributes X’s origins to Ancient Romans and Greeks. He begins a chapter on X by saying that the English alphabet probably doesn’t even need the letter. It can be substituted with a Z in words like ‘xylophone’, for instance.

“Where it has become irreplaceable is when it stands on its own: ‘x’ for a kiss, ‘x’ for the unknown algebra, ‘x’ for multiplication,” and so on, he says.

Rosen notes that the letter’s journey to the modern world, say in the US, also has a relation to the slave trade, citing the example of prominent civil rights leader Malcolm X.

He changed his last name to X, as some Black people associated their existing surnames with a lack of choice in their taking on the white families’ names. For a long period, Black slaves did not have surnames. It was, therefore, shunned by some in recognition of the fact that their original names were lost when they were dehumanised through the act of being forcibly uprooted from their lives and culture.

Rosen adds that many of the indentured workers who were brought to the US in the 17th Century were illiterate and had to sign their papers with ‘X’, as a cross was easy to copy. They would be signing into contracts that made them work for several years to repay the “cost” of their trips to North America. Some went willingly, others did not. He cites an example of a Scottish man who was taken on a ship but returned home and sued his kidnappers. “Thousands of ‘X’s helped build America. Thousands of ‘X’s perished before they could,” he writes.

Today, X has further been adopted as a symbol of fluidity by some queer communities, with genderqueer people often adopting the honorific ‘Mx.’ instead of choosing from the binary of ‘Mr.’ or ‘Mrs’.