How Did X Become the Unknown (and so much else)?

A truly X-cellent and X-ceptional video…
↓↓↓ More info and sources below ↓↓↓

Despite being one of the rarest letters in English, the letter X is everywhere. We sign letters with it, we rate movies with it, we name all sorts of things after it. We’re kind of obsessed with it. And that’s probably all thanks to math, where X stands for the unknown. Let's explore the bizarre history of how X took on this role…

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[besmart]

So now you know how X took over math, but let's give it some love in regular language: Post your favorite word containing X below! Mine is *equinox*

[DeclanMBrennan]

X also implies precision. In carpentry and on maps, it allows one to define an exact point with two crossing lines.

[dcarbs]

8:10 X is important in printing because it reaches all 4 corners equally. It is the standard by which all letters are measured in setting a typeface. From it you can calculate descenders (e.g. length of the tail on letter 'g'), ascenders (e.g. height of a letter 'h') and differing widths of letters (e.g. 'i' is thinner than 'd'), to set the spacing of words and lines when letters were physical blocks plated with ink. The principles still apply in the digital equivalent. Different typefaces take up different amounts of space on a printed page (or screen) depending on their dimensions relative to the standard 'X'.

[THETRIVIALTHINGS]

Saying X three times, reveals the mystery of creation of life too. Very mysterious.

[Harryify]

I always thought we used x because it's rare in natural language use so that you can easily distinguish math from any letters used for the description.

[LangThoughts]

6:30 Actually, in older Spanish (as in Modern Portuguese), a Sh sound did exist, which was spelt with an X. It fused with Spanish J in sound, and was thus replaced with J (except in some words). This is why in many indigenous languages of Latin America, the Sh sound is spelled with X, and why the name "Mexico", which comes from Nahuatl, is pronounced in Spanish as if it is Mejico.

[gregsquires]

Given Descartes's decision to use letter at the beginning of the alphabet for known constants and end of the alphabet for variables, it makes sense to me that x is used more than z. I bet "a" shows up more than "c" too.

[ripwolfe]

In algebra, my thought was just as `a` is the first letter of the `abc` trifecta that starts the alphabet, and `x` is the first letter of the `xyz` trifecta that ends the alphabet, then `a` and `x` are the first choices for constants and variables, respectively.

[junovzla]

6:42 actually Old Spanish did have a letter to represent the SH sound, it was the letter X! this is because the sequence KS from Latin turned into a sh sound in Old Spanish (like in "laxius" > "lexos"), which still existed in the 1500s and 1600s, but which shifted to a H sound in modern Spanish ("lexos" > "lejos"). It is now spelled as J because the Old Spanish letter J represented a ZH sound (similar to the SI in vision), but this sound also became H in modern Spanish so there was no point in keeping the distinction in writing, and since J was more common all of the X got replaced with J, except in a few words like México, which is pronounced as tho it was written Méjico.

In Portuguese and Catalan, which are both closely related to Spanish, the letter X is still pronounced as the SH sound, tho now Portuguese prefers spelling it as CH for similar reasons to the ones that led Spanish to prefer J for the H sound

Now this is all really simplified and dumbed down to the best of my abilities but there's still a whole lot of stuff that could be explained in more detail. My point is just that Spanish already had the X letter for the Arabic SH sound, so there's no need to say they borrowed Greek Chi, which adds more force to the hypothesis by making it simpler

[complexcreations]

At 2:35 The first '=' at the bottom should instead be '+' and at 5:12 it should be x² - 3x = 2.

[SupercriticalSnake]

"X" is like an edgier version of "Q". Oh, your letter is a circle with a little diagonal line through it and it's used for sounds that other letters already make? Here's a bigger diagonal line with another diagonal line through it and it's sometimes pronounced as a freakin' "Z". Also, it hangs out with the weird letters in the back of the alphabet, not those respectable letters like "R", "S", and "T".

[boled._.rce]

Elon Musk has a weird obsession with X

[shada]

I think it's important to include the shape of X, it's a very satisfying & easy thing to draw. Like X is more fun to draw than +, that's a little weird.

[donbrunodelamancha]

You spoke the logic and philosophy of X in the first few minutes of this very episode. It is, it’s very scarcity in language, called it into used in mathematics. What better integer placeholder to use than something that is so uncommonly used, it cannot be confused with any other use? Philosophy led the way X. It’s scarcity made it the perfect place holder for unknown because you cannot be confused for anything else.

[gusamamon]

Additionally, X is used to indicate negation or important things (as in "X marks the spot"). By the way, in Mexican Spanish, calling something or someone X ("equis") means that it is irrelevant or indifferent (like saying "meh" or "whatever").

[MegaMinerd]

Interesting video. I knew pieces of this, but it's nice to see it all put together. Minor critique though. I'm studying Arabic, and I noticed that شيء is incorrectly written left to right at 6:20.

[ggtt]

Fun fact, today the sound of "X" in the modern Greek alphabet is written like "Ξ", which is almost identical to the ancient Phoenician one at 1:29!

[PuzzledMonkey]

The Greek letter for x is Ξ (capital) or ξ, lower case, not Χ. It is pronounced ksee. Chi is a fricative, like the ch in German Bach.

The x in old Spanish was in fact pronounced like English sh, so such a translation from Arabic would have made perfect sense.

[akhilyadav]

3:01 I don't know about Brahmagupta, but as a child, my father told me how ancient mathematicians used seeds of plants to refer to unknowns in equations.
Upto this day, the term for algebra in Hindi is "बीजगणित" [beejganit], where "beej" means "seed" and "ganit" means "mathematics".

[constancialazarra]

Most people: *watches video out of curiosity*

Me: THE CONTINUOUS SEARCH OF A PERSON THAT ADDED LETTERS TO MATH SHALL BEGIN