If I've understood correctly, Spanish phonology underwent this change from Latin with respect to the sound /ks/:

⟨x⟩ /ks/  →  ⟨x⟩ /ʃ/  →  ⟨x⟩ /ʃ/ ↘  
                                 ⟨j⟩ /x/
    ...  →  ⟨j⟩ /ʒ/  →  ⟨j⟩ /ʃ/ ↗ 

However there are a number of Spanish words that are spelled with an x, and pronounced as /ks/ (realised as [ks], [gs] or [s], depending on context and register):

  • exacto (EXACTUS)    vs fijar (FIXUS)
  • exento (EXEMPTUS)   vs ejercicio (EXERCITIUM)
  • exhibir (EXIBERE)    vs mejilla (MAXILLA)
  • exhortar (EXHORTARI) vs lejos (LAXIUS)
  • exultar (EXSULTO)    vs lujuria (LUXUS)

Some x words even have doublets spelled and pronounced as j /x/:

  • (TEXERE) textil, texto, textura        | tejer, tejido
  • (LAXARE) laxitud, laxante           | dejar, dejadez
  • (COXINUM) coxal                   | cojín
  • (ANNEXUS) anexo, anexar, anexionar | anejo, anejar
  • (PROXIMUS) próximo                | prójimo

I imagine these words might have retained the x spelling due to very popular use, or them being borrowed as learned Latin words and not 'naturally' inherited into the language (e.g. axón), but:

Why (and when) did these words retain (or regain) their /ks/ pronunciation when in most similar words it was lost?

Examples: Spanish Vocabulary: An Etymological Approach, David Brodsky

  • 1
    The pairs like próximo/prójimo generally are a natural evolution (prójimo) along with a reimport from Latin that occurred after the sound change(s) were no longer productive. In almost all cases I can think of, the pairs end up with different, albeit related, uses (probably the easiest to see this in is lugar/local. Notice the /ks/ sound was preserved with the prefix ex- and before consonants. Intervocalically is where the shifts happened.) The date of reimport will be different for each word, but obviously necessarily will be after the sound changes were no longer productive. Feb 24, 2018 at 21:36
  • 1
    The letter X has had multiple pronunciations since at least the first orthography, the spelling change was really more to represent /x/ with j and retain x for /ks/, rather than to get rid of X. Feb 24, 2018 at 21:38
  • I don't understand what you are asking for, do you want to know when the "X" represented a the "KS" sound or when words with "x" started to be pronounced like "KS" ?
    – Mike
    Feb 27, 2018 at 19:05
  • (Assuming these words spelled with an x were at one time not pronounced like /ks/) I would like to know when words spelled with an x started being pronounced /ks/.
    – jacobo
    Feb 27, 2018 at 19:12
  • @guifa "Notice the /ks/ sound was preserved with the prefix ex- and before consonants." This doesn't seem to be completely true. See, for example, ejercicio, ejemplo, ejecutar whose older orthographies were exercicio, exemplo, executar. "The letter X has had multiple pronunciations since at least the first orthography" Do you have a source for this?
    – jacobo
    Apr 30, 2018 at 12:29

1 Answer 1


As guifa says in a comment, the sound change of /ks/ to /x/ was blocked when the letter x was followed by a consonant. In these circumstances /ks/ was generally reduced to /s/, with the /ks/ pronunciation re-emerging as a form of hypercorrection:


The evidence indicates that this Latin letter represented [ks]. The development of the sound in Vulgar Latin and in the Romance languages varied from region to region, with more changes occurring in Spanish than in any other case.

In Castilian territory the [ks] > [js] > [sj] > [š]. This last phone leveled with [ž] from Latin J and G (e, i) in the fifteenth and sixteenth centuries, and the resulting [š] gradually became [χ] by 1650. In the nineteenth century the Spanish Royal Academy did away with the spelling x, except in Latinisms such as examen, sexta, and words such as dixe are now spelled with j (dije). In Mexico, especially, the x has been retained in words of Indian origin to represent a primitive [š] (Mexico, Xalapa, Oaxaca), now [χ], and in Yucatan one still hears the [š] (Uxmal) among the Maya- speaking inhabitants or among foreigners ...


It is to be noted that the evolution of X to an ultimate [χ] did not take place when it was supported by a consonant as in FRÁX(I)NU > fresno, SÉXTA > siesta, and where X has been retained before a consonant, generally represents [s] (extraño [estráño], experiencia [esperjénsja]).135

In the other Romance languages the -X- [ks] usually became a sibilant or retained its original Latin value. In Catalan and Portuguese the descendents are [s] (x) and [s] (ss) and the letter X has been extended to represent [š] of other origins than Latin X:

Arabic [š] (P. xadrez C. aixedres), Latin -PS- (P. C. caixa). In Catalan the [č] is represented normally by tx.136

135. In the latter type [s] (= x preceding consonant), hypercorrection often produces [ks] or [gs] through pedantic school teaching, i.e. sexta [séksta] and extrano [ekstráno]. This is not the popular pronunciation however.

Thus, words with an 'x' spelling come under three categories in Spanish:

    • ...xV... (x followed by vowel, naturally inherited from Latin to Spanish)
      ⟨x⟩ /ks/ → ⟨x⟩ [js] → ⟨x⟩ [sj] → ⟨x⟩ /ʃ/ → ⟨j⟩ /ʃ/ → ⟨j⟩ /x/

      e.g. exemplusexemploejemplo

    • ...x... (loanword at time when "x" was pronounced /ʃ/)
      ⟨x⟩ /ʃ/ → ⟨j/x⟩ /ʃ/ → ⟨j/x⟩ /x/

      e.g. (Nahuatl: Mēxihco → ) MéxicoMéjicoMéxico
      e.g. (Catalán: boxusboix → ) boxboj

  1. ...xC... (x followed by consonant, naturally inherited from Latin to Spanish)
    ⟨x⟩ /ks/ → ⟨x⟩ [s] → ⟨x⟩ [ks]~[gs]~[s]

    e.g. expertusexperto

  2. ...x... (x, learned Latin borrowing)
    ⟨x⟩ /ks/ → ⟨x⟩ [ks]~[gs]~[s]

    e.g. proximuspróximo


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