Learning Spanish I identified some phonotactic rules of thumb how words from Latin transform into Spanish. These rules sometimes help me recognize the Latin root of an unknown Spanish word and help me understand it that way. They are also useful for memorizing new vocabulary. These are the rules I've found:

  1. -us and -um in the ending → -o

    • MANUS → mano
    • OVUM → huevo
  2. ctch:

    • examples:
      • DIRECTE → derecha
      • TECTUM → techo
      • PECTUS → pecho
      • OCTO → ocho
    • exception:
      • CORRECTUS → correcho correcto
  3. f in the beginning → h:

    • examples:
      • FACERE → hacer
      • FABULARE → hablar
      • FUMUS → humo
    • exceptions:
      • FIRMARE → hirmar firmar
      • quite interesting, because of the analogy to FUMUS: FUMARE → humar fumar
  4. lio / liajo / ja:

    • examples:
      • FILIUS / FILIA → hijo / hija
      • MULIER → mujer
      • FOLIA → hoja
    • exception:
      • ANOMALIA → anomaja anomalía
      • FAMILIA → famija familia
  5. st / sp / sc in the beginning → est / esp / esc:

    • examples:
      • STARE → estar
      • STUPIDUS → estúpido
      • SCHOLA → eschuela
      • SPECIALITAS → especialidad
      • SPONGEA → esponja
  6. long oue:

    • examples:
      • OVUM → huevo
      • SCHOLA → eschuela
      • (EGO) DORMO → (yo) duermo
      • CORPUS → cuerpo
      • FOCUS → fuego
    • exception:
      • DORMITORIUM → duermitorio dormitorio
  7. pl / cl in the beginning → ll:

    • examples:
      • PLUERE → llover
      • CLAMARE → llamar
    • exception:
      • PLUMA → lluma pluma
  8. double consonants become single consonants, except for rr:

    • ACCEPTARE → aceptar
    • COMMUNIS → comun
    • CURRERE → correr

However, there are exceptions from these rules (I have named some alongside the examples). In some cases I have read that this is a sign that the word has come into Spanish via ways of written communication, while these phonetic transformations mentioned above are a sign that the respective words have made their way into Spanish via an oral route.

Besides this historic reason, are there any known systematic lexical regularities for exceptions of these rules? Or do I just need to know the loan-history of the word to predict whether it is transformed in a way above or not?

  • 1
    Apropos dormitorium: the verb dormir is an o → ue stem change, so that’s something. Aug 26, 2020 at 12:46
  • 1
    Note though that we say ahumar for 'smoke' as in salmon ahumado.
    – fedorqui
    May 1, 2021 at 21:31

1 Answer 1


My reference work in this matter is From Latin to Spanish: Historical phonology and morphology of the Spanish language, by Paul M. Lloyd. Roughly half of the book is about morphology, the other half about phonology. Undoubtedly there are other good works on the subject, but this looks comprehensive enough to me.

Lloyd mentions all of these rules you've found in some way or another, but he does note that, besides loans etc., there are some instances where we don't know enough to formulate any rule with certainty. Off the top of my head, he mentions that the Vulgar Latin voiced stops /b/ /d/ /g/ in intervocalic position evolved in unpredictable ways, and that studying /g/ especially was difficult because there weren't many instances of it left to begin with; moreover, the change from stop to fricative that these three consonants were experiencing is only apparent in old texts in the case of /b/ because scribes sometimes exchanged B and V.

One extra problem is that "Spanish" was not one language; there were several competing dialects, and while the major northern variant (Castilian) ended up becoming the standard, there are many instances when a word evolved differently in different dialects, and the modern form might come from any of these.

There are many, many more exceptions to the rules you found, mostly having to do with reborrowings from (medieval) Latin and technical words (leading to pairs like pecho vs. pectoral and hijo vs. filial).

Note that your rule #6 is wrong. It was not the long vowels of Classical Latin which ended up as diphthongs in Spanish, but the short ones, which in Proto-Romance were actually not short (quantity having been lost as a distinction) but open-mid /ɛ/ and /ɔ/, contrasting with close-mid /e/ and /o/. (You cite Latin OVUM as example, which had a long ō in classical times, but this was shortened later.) The open-mid vowels of Spanish diphthongized when stressed.

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