Old Spanish

Among the consonants, there were seven sibilants, including three sets of voiceless/voiced pairs:

• Voiceless alveolar affricate /t͡s̻/: represented by ⟨ç⟩ before ⟨a⟩, ⟨o⟩, ⟨u⟩, and by ⟨c⟩ before ⟨e⟩ or ⟨i⟩
• Voiced alveolar affricate /d͡z̻/: represented by ⟨z⟩
• Voiceless apicoalveolar fricative /s̺/: represented by ⟨s⟩ in word-initial and word-final positions and before and after a consonant, and by ⟨ss⟩ between vowels
• Voiced apicoalveolar fricative /z̺/: represented by ⟨s⟩ between vowels and before voiced consonants
• Voiceless postalveolar fricative /ʃ/: represented by ⟨x⟩ (pronounced like the English digraph ⟨sh⟩)
• Voiced postalveolar fricative /ʒ/: represented by ⟨j⟩, and (often) by ⟨g⟩ before ⟨e⟩ or ⟨i⟩ (pronounced like the si in English vision)
• Voiceless postalveolar affricate /t͡ʃ/: represented by ⟨ch⟩

The set of sounds is identical to that found in medieval Portuguese and almost the same as the system present in the modern Mirandese language.

The Modern Spanish system evolved from the Old Spanish one with the following changes:

1. The affricates /t͡s̻/ and /d͡z̻/ were simplified to laminodental fricatives /s̻/ and /z̻/, which remained distinct from the apicoalveolar sounds /s̺/ and /z̺/ (a distinction also present in Basque).
2. The voiced sibilants then all lost their voicing and so merged with the voiceless ones. (Voicing remains before voiced consonants, such as mismo, desde, and rasgo, but only allophonically.)
3. The merged /ʃ/ was retracted to /x/.
4. The merged /s̻/ was drawn forward to /θ/. In some parts of Andalusia and the Canary Islands, however (and so then in Latin America), the merged /s̺/ was instead drawn forward, merging into /s̻/.

Changes 2–4 all occurred in a short period of time, around 1550–1600. The change from /ʃ/ to /x/ is comparable to the same shift occurring in Modern Swedish (see sj-sound).

The Old Spanish spelling of the sibilants was identical to modern Portuguese spelling, which, unlike Spanish, still preserves most of the sounds of the medieval language, and so is still a mostly faithful representation of the spoken language. Spanish spelling was altered in 1815 to reflect the changed pronunciation:[1]

• passar "to pass" vs. casar "to marry" (Modern Spanish pasar, casar, cf. Portuguese passar, casar)
• osso "bear" vs. oso "I dare" (Modern Spanish oso in both cases, cf. Portuguese urso [a borrowing from Latin], ouso)
• foces "sickles" vs. fozes "base levels" (Modern Spanish hoces in both cases, cf. Portuguese foices, fozes)
• coxo "lame" vs. cojo "I seize" (Modern Spanish cojo in both cases, cf. Portuguese coxo, colho)
• xefe "chief" (Modern Spanish jefe, cf. Portuguese chefe)
• Xeres (Modern Spanish Jerez, cf. Portuguese Xerez)
• oxalá "if only" (Modern Spanish ojalá, cf. Portuguese oxalá)
• dexar "leave" (Modern Spanish dejar, cf. Portuguese deixar)
• roxo "red" (Modern Spanish rojo, cf., Portuguese roxo "purple")
• fazer or facer "make" (Modern Spanish hacer, cf. Portuguese fazer)
• dezir "say" (Modern Spanish decir, cf. Portuguese dizer)
• lança "lance" (Modern Spanish lanza, cf. Portuguese lança)

The Old Spanish origins of jeque and jerife reflect their Arabic origins, xeque from Arabic sheikh and xerife from Arabic sharif.

The letters ⟨b⟩ and ⟨v⟩ still had distinct pronunciations; ⟨b⟩ still represented a stop consonant [b] in all positions, and ⟨v⟩ was likely pronounced as a voiced bilabial fricative or approximant [β] or [β̞] (although word-initially, it may have been pronounced [b]). The use of ⟨b⟩ and ⟨v⟩ in Old Spanish largely corresponded to their use in Modern Portuguese, which distinguishes the two sounds except in northern European dialects. The phonological distinction of the two sounds also occurs in several dialects of Catalan (central and southern Valencian, an area in southern Catalonia, the Balearic dialect and Alguerese), though not in Standard Catalan from eastern Catalonia. When Spanish spelling was reformed in 1815, words with ⟨b⟩ and ⟨v⟩ were respelled etymologically to match the Latin spelling whenever possible:

• aver (Modern Spanish haber, compare Latin habēre, Portuguese haver)
• caber (Modern Spanish caber, compare Latin capere, Portuguese caber)
• bever (Modern Spanish beber, compare Latin bibere; Portuguese beber < older bever)
• bivir or vivir (Modern Spanish vivir, compare Latin vīvere, Portuguese viver)
• amava (Modern Spanish amaba, compare Latin amābam/amābat, Portuguese amava)
• saber (Modern Spanish saber, compare Latin sapere, Portuguese saber)
• livro (Modern Spanish libro, compare Latin līber, Portuguese livro)
• palavra (Modern Spanish palabra, compare Latin parabola, Portuguese palavra)

Many words now written with an ⟨h⟩ were written with ⟨f⟩ in Old Spanish, but it was likely pronounced [h] in most positions (but [ɸ] or [f] before /r/, /l/, [w] and possibly [j]). The cognates of the words in Portuguese and most other Romance languages have [f]. Other words now spelled with an etymological ⟨h⟩ were spelled without any such consonant in Old Spanish: haber, written aver in Old Spanish). Such words have cognates in other Romance languages without [f] (e.g. French avoir, Italian avere, Portuguese haver with silent etymological ⟨h⟩):

• fablar (Modern Spanish hablar, Portuguese falar)
• fazer or facer (Modern Spanish hacer, Portuguese fazer)
• fijo (Modern Spanish hijo, Portuguese filho)
• foces "sickles", fozes "base levels" (Modern Spanish hoces, Portuguese foices, fozes)
• follín (Modern Spanish hollín)
• ferir (Modern Spanish herir, Portuguese ferir)
• fiel (Modern Spanish fiel, Portuguese fiel)
• fuerte (Modern Spanish fuerte, Portuguese forte)
• flor (Modern Spanish flor, Portuguese flor)

Modern words with ⟨f⟩ before a vowel mostly represent learned or semi-learned borrowings from Latin: fumar "to smoke" (compare inherited humo "smoke"), satisfacer "to satisfy" (compare hacer "to make"), fábula "fable, rumor" (compare hablar "to speak"). Certain modern words with ⟨f⟩ that have doublets in ⟨h⟩ may represent dialectal developments or early borrowings from nearby languages: fierro "branding iron" (compare hierro "iron"), fondo "bottom" (compare hondo "deep"), Fernando "Ferdinand" (compare Hernando).

Old Spanish had ⟨ch⟩, just as Modern Spanish does, which mostly represents a development of earlier */jt/ (still preserved in Portuguese and French), from the Latin ct. The use of ⟨ch⟩ for /t͡ʃ/ originated in Old French and spread to Spanish, Portuguese, and English despite the different origins of the sound in each language:

• leche "milk" from earlier leite (Latin lactem, cf. Portuguese leite, French lait)
• mucho "much", from earlier muito (Latin multum, cf. Portuguese muito, French moult (rare, regional))
• noche "night", from earlier noite (Latin noctem, cf. Portuguese noite, French nuit)
• ocho "eight", from earlier oito (Latin octō, cf. Portuguese oito, French huit)
• hecho "made" or "fact", from earlier feito (Latin factum, cf. Portuguese feito, French fait)

The palatal nasal /ɲ/ was written ⟨nn⟩ (the geminate nn being one of the sound's Latin origins), but it was often abbreviated to ⟨ñ⟩ following the common scribal shorthand of replacing an ⟨m⟩ or ⟨n⟩ with a tilde above the previous letter. Later, ⟨ñ⟩ was used exclusively, and it came to be considered a letter in its own right by Modern Spanish. Also, as in modern times, the palatal lateral /ʎ/ was indicated with ⟨ll⟩, again reflecting its origin from a Latin geminate.

The Graeco-Latin digraphs (digraphs in words of Greek-Latin origin) ⟨ch⟩, ⟨ph⟩, ⟨(r)rh⟩ and ⟨th⟩ were reduced to ⟨c⟩, ⟨f⟩, ⟨(r)r⟩ and ⟨t⟩, respectively:

• christiano (Modern Spanish cristiano)
• triumpho (Modern Spanish triunfo)
• myrrha (Modern Spanish mirra)
• theatro (Modern Spanish teatro)

Word-initial [i] was spelled Y, which was simplified to letter I.

In common with other European languages before the 17th century, the letter pairs ⟨i⟩ and ⟨j⟩ and ⟨u⟩ and ⟨v⟩ were not distinguished. Modern editions of Old Spanish texts usually normalise the spelling to distinguish the pairs, as Modern Spanish does.