The Plural

In Portuguese, number — singular or plural — is marked chiefly at the end of the word, by a morpheme that originates in the -s inherited from the Latin accusative plural. The plural of nouns and adjectives follows a small set of predictable rules, conditioned by the letter (and sound) the word ends in. The one genuinely intricate area is that of nouns ending in -ão, which split across three distinct endings.

The general rule: add -s

Words ending in a vowel or an oral diphthong form the plural by simply adding -s:

Plurals in -es: nouns ending in -r, -z and -s

Words ending in -r or -z add -es; the -z ending shows its sibilant value in the plural:

Those ending in -s divide according to stress. If the word is oxytone (stressed on the final syllable, including stressed monosyllables), -es is added; if it is paroxytone or proparoxytone, it stays invariable, the number being shown only by the article:

Nouns ending in -m: -m becomes -ns

Where the singular has -m, the plural has -ns — a purely orthographic convention for writing nasality before -s:

Nouns ending in -l: -l drops and -is enters

Words ending in -l lose the -l and take -is. The result depends on the preceding vowel:

• -al, -el, -ol, -ul → -ais, -éis, -óis, -uis: animal → animais, papel → papéis (“paper”), anzol → anzóis (“fish-hook”), paul → pauis;
• unstressed -il (paroxytone) → -eis: fóssil → fósseis, réptil → répteis;
• stressed -il (oxytone) → -is: funil → funis (“funnel”), fuzil → fuzis.

Note the written accent that appears in papéis and anzóis: the resulting diphthong is stressed and open, and the accent marks it.

The case of -ão: -ões, -ães or -ãos

Nouns in -ão are where intuition fails, because a single modern ending conceals three different Latin endings that evolved in parallel. Hence the three possible plurals:

Singular	Plural	Latin origin	Type
balão, coração, nação	balões, corações, nações	-ONE(M)	-ões
pão, cão, alemão, capitão	pães, cães, alemães, capitães	-ANE(M)	-ães
mão, irmão, cidadão, órfão	mãos, irmãos, cidadãos, órfãos	-ANU(M)	-ãos

The -ões pattern is by far the most productive: it is the one taken by almost all new nouns and by the overwhelming majority of existing ones. The -ães group is small and closed; the -ãos group gathers mainly paroxytones (órfão “orphan”, órgão “organ”, sótão “attic”) and a few very old words (mão “hand”, irmão “brother”).

Vowel opening: metaphony

In one group of masculine nouns, the plural changes more than the ending: it opens the stressed vowel, close [o] in the singular and open [ɔ] in the plural. This is a relic of metaphony (vowel inflection conditioned by the final Latin vowel) still heard today, and it distinguishes pairs such as these:

Singular	Plural	Meaning
*ovo* [ˈo.vu]	*ovos* [ˈɔ.vuʃ]	egg(s)
*porco* [ˈpoɾ.ku]	*porcos* [ˈpɔɾ.kuʃ]	pig(s)
*osso* [ˈo.su]	*ossos* [ˈɔ.suʃ]	bone(s)
*olho* [ˈo.ʎu]	*olhos* [ˈɔ.ʎuʃ]	eye(s)

The opening is not general: bolo [ˈbo.lu] keeps its close o in the plural bolos [ˈbo.luʃ] . It is a lexical list, which the native speaker knows by ear.

Special cases

Compound nouns inflect according to the nature of their parts: both elements pluralise in noun + noun or noun + adjective compounds (couve-flor → couves-flores “cauliflower”, guarda-noturno → guardas-noturnos “night watchman”), but only the first when the second qualifies it or when the compound is verb + noun (guarda-chuva → guarda-chuvas “umbrella”). Diminutives in -zinho pluralise both parts: pão → pãezinhos, flor → florezinhas. Words ending in -x are invariable (o tórax → os tórax “thorax”), as are many loanwords not yet adapted.