It seems that the original intent of the letter 'X' was to pronounce the phoneme [k^h] in Classical Greek but evolved over time to be [ks].

My question is: How come there are so many European languages that use the sounds [k] and [s] together, when there are so few non-European languages that use the sounds together so frequently?

There doesn't appear to be any innate affricate connection between the two sounds, unlike the way [t͡ʃ] and [d͡ʒ] appear independently in many world languages.

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    I believe x was used for /ks/ by Greeks too, in archaic times: some used it for /ks/, others for /kʰ/.
    – Cerberus
    Jun 21, 2013 at 17:38
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    I think you're right, but what I am more interested in is how did the sound combination of /ks/ become so widespread, or how come the average person doesn't think of it like a consonant cluster? I can't find any example of anther digraph like this outside of European languages; it's very unusual in Japanese, Chinese, Korean, and Arabic for Example. In Hindi, it appears only in a few names, like Lakshmi. Jun 21, 2013 at 19:19
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    @CayetanoGonçalves: In Sanskrit, the string /kṣ/ is very common. In fact, there's a rule in Panini about it, the "Ruki" rule: an /s/ immediately after any of the four phonemes /r/, /u/, /k/, and /i/ is automatically retroflexed to a /ṣ/. There are a lot of those words around in Hindi today. But that's not really a special letter, just a peculiar phonological feature of Sanskrit; in an abugida like Devanagari, there are special letters for all consonant clusters.
    – jlawler
    Jun 21, 2013 at 19:42
  • The same phenomenon occurs with English [kw] for 'q' and a couple of other languages. Jun 22, 2013 at 1:08
  • Devanāgarī arguably also has an ‘x’: the character for /kṣ/ is the only consonant compound in which it's hard to see any trace of either component. (In /jñ/, the /j/ is fairly clear but not the /ñ/.) May 16, 2016 at 7:24

1 Answer 1


It came about like this. (Details about Greek here)

When Greeks adopted the Punic abjad into an alphabet, they changed a lot of the letters, and added some new ones. The Punes hadn't needed vowel letters, for instance, due to the nature of the language, but the Greeks did. On the other hand, the Greeks didn't need the post-velar and emphatic consonants of Semitic, so they used those letters for vowels.

Alpha, for instance, represented a post-velar consonant -- glottal stop [ʔalif] -- in Punic (and still does in Hebrew and Arabic), but it represents the vowel /a/ in the Greek alphabet, and has since then in the Latin.

One of the clever things the Greeks did was invent special letters for combinations of stops and the sibilant /s/. There were three of them, one in each of the three Greek places of articulation -- labial, dental, and velar.

  • The Labial + S letter is Psi (Ψ ψ /ps/), which was the letter you used when any of the three labial stops -- voiceless Pi (Π π /p/), aspirated Phi (Φ φ /pʰ/), or voiced Beta (Β β /b/) -- occurred before Sigma (Σ σ ς /s/).

  • The Dental + S letter is Zeta (Ζ ζ /ts/), which got voiced to /dz/, metathesized to /zd/ and thence to /z/ in historic times.

  • The Velar + S letter is Xi (Ξ ξ /ks/), which was the letter you used when velar stops occurred before Sigma. (Note, by the way, that this letter is not "X" but "Ξ".)

So why did they need special letters for sounds before /s/? Because

  1. Greek was heavily inflected, and many of the suffixes began with /s/.
  2. Many of the roots ended in stop consonants, right before adding suffixes.
  3. Before /s/, the three-way voiced/voiceless/aspirated stop distinction neutralized;
    i.e, there was no difference and they all came out the same.

So it was sensible to use a special stop for that common combination. When the Greek alphabet was later adapted for Latin, Ψ (psi) didn't make it into Latin at all, but Ξ (ks) did, and was used for the /ks/ cluster. However, they changed the shape of the letter. Having no need for a letter for aspirated /kʰ/ in Latin, they used Χ instead of Ξ, possibly because it was easier to write.

So it's an accident. You can find out all about the history of each letter in any good encyclopedia, btw. Especially David Crystal's Cambridge Encyclopedias, of Language and of the English Language.

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    It may be relevant that there are many Latin words whose stem ends in -c or -g, and whose nom. sing. therefore ends in -x; but rather few stems ending -p, so the nom. sing -ps, though it certainly occurs, is not particularly common.
    – Colin Fine
    Jun 21, 2013 at 23:09
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    @ColinFine: That is true: -ps- and -ts- are very rare in Latin, almost all Greek loan words. Lawler: Good answer. One thing to note: I believe there is no consensus about the pronunciation of zeta. There is evidence suggesting dental-sibilant, but also sibilant-dental. And different pronunciations may very well have coexisted between regions.
    – Cerberus
    Jun 23, 2013 at 16:06
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    About the Ξ vs X : The story is well known, and did not come from the Romans as you say but among the Greeks themselves. There were several archaic greek alphabets with different innovations compared to the phoenician alphabet. Modern greek alphabet is based on the Eastern Greek alphabet, used in Athens, while the Etruscan took their alphabet from Greek colonies using the western version. They among other things, they diferred on how to write ksi(E:Ξ W:Χ) and khi(E:Χ W:Ψ) Jun 24, 2013 at 15:37
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    Emperor Claudius perceived the lack of an equivalent to "psi" as a defect in the Latin script, so he invented new letters for bs/ps, another for "w" sound (as the Greek digamma) and another for the "y" sound (a real innovation, showing the keen amateur linguist he was). Too bad they didn't catch on and were forgotten after his demise...
    – Joe Pineda
    Mar 7, 2014 at 16:29
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    The Greeks did not “invent special letters for combinations of stops and the sibilant /s/”, pace jlawler. This is true only of ψ. Z and Ξ , like most of the other letters, were taken from the Phoenician (not “Punic”=Cartheginian) alphabet. It is possible (though not certain) that the antecedent of Z was pronounced as /dz/, and the antecedent of Ξ as /ts/ in Phoenician. This is, however, debated amongst Semitists.
    – fdb
    Mar 7, 2014 at 17:30

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