Sibilants and hushing sounds

Portuguese has four sibilant consonants, paired by voicing and by place of articulation: the alveolar /s/ and /z/ (the sibilants proper) and the palato-alveolar /ʃ/ and /ʒ/ (the hushing sounds). The relationship between these four sounds and the spelling is one of the knottiest in the language, because the writing system preserves medieval distinctions that pronunciation has long erased.

Phoneme	Usual spellings	Example
[s]	*s-*, *-ss-*, *c* (before *e/i*), *ç*	*passo* [ˈpasu] (step)
[z]	*z*, intervocalic *-s-*	*casa* [ˈkazɐ] (house)
[ʃ]	*ch*, *x*; *-s/-z* in the coda	*chave* [ˈʃavɨ] (key)
[ʒ]	*j*, *g* (before *e/i*); voiced coda	*jogo* [ˈʒoɣu] (game)

s and z: the merger of the old series

Medieval Galician-Portuguese distinguished two series of alveolar sibilants. On one side, the apico-alveolar /s̺/ and /z̺/, written -ss- and -s-; on the other, the dental affricates /ts/ and /dz/, written c/ç and z. These were four distinct sounds: passo /ˈpasso/ was not paço /ˈpatso/, and coser (to sew) /koˈzeɾ/ was not cozer (to cook) /koˈdzeɾ/.

Between the 15th and 17th centuries the affricates lost their initial stop and became plain fricatives; the two series then collapsed into one. Hence the present system: passo and paço are now homophones [ˈpasu] , and coser and cozer differ only in the surrounding vowel. The spelling, however, stayed put: ç, ss, s and z survive as relics of extinct phonetic contrasts — which is exactly why they still have to be memorised.

ch and x: meeting in [ʃ]

The story of ch repeats the pattern. In Galician-Portuguese, ch stood for the affricate /tʃ/, inherited above all from the Latin clusters cl-, pl-, fl- (Lat. CLAMARE → chamar, PLENUM → cheio, FLAMMAM → chama). The letter x, meanwhile, already had the value of the fricative /ʃ/. They were, then, different sounds.

Across most of the territory the affricate /tʃ/ de-affricated and merged with /ʃ/. In standard European Portuguese, chave (key) and xaile (shawl) begin with the same sound [ʃ] . Once again, the orthography keeps a memory that the phonology no longer realises.

The letter x is, even so, the most unpredictable in the alphabet: besides [ʃ] it can stand for [s], [z] or [ks], and no simple rule decides between them.

Value	Examples	Gloss
[ʃ]	*xaile, peixe, baixo*	shawl, fish, low
[s]	*próximo, trouxe, máximo*	next, brought, maximum
[z]	*exame, exato*	exam, exact (*ex-* + vowel)
[ks]	*táxi, fixo, tórax*	taxi, fixed, thorax

The European syllable-final [ʃ]

The trait that most readily marks European Portuguese for the untrained ear is the palatalisation of coda sibilants. When -s or -z closes a syllable, it is not [s] but a hushing sound whose voicing depends on what follows:

• before a pause or a voiceless consonant, it surfaces as [ʃ]: paz [ˈpaʃ] (peace), estes [ˈeʃtɨʃ] (these);
• before a voiced consonant, it assimilates to [ʒ]: os livros [uʒ ˈlivɾuʃ] (the books);
• before a vowel — even across a word boundary — it voices to [z]: os amigos [uz ɐˈmiɣuʃ] (the friends).

This rule runs through the whole of speech: the plural, the verb ending -mos, the articles os/as — all end in that hushing sound. Combined with the reduction of unstressed vowels, it gives European Portuguese the dense, “closed” texture that so often makes it sound, to the uninitiated, like a Slavic language.

In short

Four phonemes, but a spelling that records six or seven inherited distinctions: the mismatch between s/ss/c/ç/z and ch/x is, in large part, the written record of oppositions that time has dissolved. And the syllable-final [ʃ], far from a minor detail, is one of the sonic signatures of the European pronunciation.