Stress and Tonicity

In every Portuguese word of more than one syllable, one syllable is pronounced more prominently than the rest: this is the stressed (tonic) syllable, the seat of the stress accent. It must not be confused with the written accent (´, `, ^) — the orthographic mark that signals that syllable only in certain cases. Tonicity is a fact of the spoken language; it is present in every word, whether or not the word carries a written accent.

What marks out the stressed syllable

Unlike Spanish, European Portuguese signals stress chiefly not through sheer loudness but through duration: the stressed vowel is markedly longer, and the surrounding unstressed vowels reduce — they shorten, close, and may even vanish. Pitch and intensity play a secondary part. It is this combination of a full, long vowel ringed by weak ones that gives European Portuguese its characteristic clipped rhythm.

Free stress, within a window

Portuguese has free stress: unlike French (always on the last syllable) or Czech (always on the first), the position of the accent is not fixed and must be learned word by word. That freedom is nonetheless bounded — the accent always falls on one of the last three syllables, the so-called three-syllable window. According to its position, the Portuguese grammatical tradition sorts words into three types:

Type	Stress on the…	Example	Phonetics
aguda (oxytone)	last syllable	*café* (coffee)	[kɐˈfɛ]
grave (paroxytone)	penultimate syllable	*mesa* (table)	[ˈmezɐ]
esdrúxula (proparoxytone)	antepenultimate syllable	*médico* (doctor)	[ˈmɛdiku]

The overwhelming majority of Portuguese words are grave: this is the unmarked pattern, the one a reader assumes by default. Proparoxytones are the rarest and always carry a written accent (lâmpada “lamp”, sábado “Saturday”, árvore “tree”). A fourth position — before the antepenult — arises only when a word takes unstressed pronouns (entregando-no-lo), giving the rare sobresdrúxulas.

Stress sets words apart

The position of the accent is distinctive: shifting it can change a word’s meaning, and sometimes its grammatical class. The same letters, stressed on different syllables, spell different words.

The same play opposes número [ˈnumɨɾu] (the noun “number”), numero [nuˈmɛɾu] (“I number”) and numerou [numɨˈɾo] (“he numbered”) — three stress patterns, three forms. Without the accent the writing would be ambiguous; resolving exactly that ambiguity is what the written accent is for.

Where it tends to fall

Free though it is, stress follows strong tendencies tied to the end of the word, and it is on these that the spelling system rests. In brief:

• words ending in -a, -e, -o (and -as, -es, -os, -am, -em) are by default grave and need no accent: casa, pente, livro, cantam;
• words ending in -i, -u, -l, -r, -z or in a nasal diphthong are by default aguda: javali, capaz, animal, amor, então.

The written accent marks only the exceptions to these tendencies: an oxytone ending in an open vowel (café, avó, José) or a paroxytone ending in an uncommon consonant (túnel, açúcar, fácil). Proparoxytones, being exceptions one and all, are accented without reserve.

Stress and morphology: the verbs

In verbs, tonicity is morphological: it shifts position across the conjugation, depending on whether the strong syllable falls on the stem or on the ending. In the present indicative the nós and vós forms are arrhizotonic — the accent moves onto the ending — while in the other persons it stays on the stem (rhizotonic):

eu	**fa**lo [ˈfalu]
tu	**fa**las [ˈfalɐʃ]
ele/ela	**fa**la [ˈfalɐ]
nós	fa**la**mos [fɐˈlɐmuʃ]
vós	fa**la**is [fɐˈlajʃ]
eles/elas	**fa**lam [ˈfalɐ̃w̃]

Notice how, as the accent shifts in falamos, the first syllable reduces from [ˈfa] to [fɐ] : tonicity directly governs the quality of the vowels.

Stress, rhythm and reduction

It is this dependence that makes European Portuguese a stress-timed language: the intervals between stressed syllables tend to even out in time, and the unstressed syllables compress to keep pace. Hence the intense vowel reduction that so hampers word recognition for learners. Function words — articles, prepositions, clitic pronouns — are usually unstressed and lean phonetically on a neighbouring word, forming a single stress group with it.