Diphthongs

A diphthong is a sequence of a vowel and a semivowel pronounced within a single syllable, in one impulse. In Portuguese the semivowel is always one of two: the semivocalic i [j] or the semivocalic u [w] . When the same letters instead stand for a full vowel forming a syllable of its own, there is no diphthong but a hiatus: compare pai [ˈpaj] (“father”, one syllable) with pa-ís [pɐˈiʃ] (“country”, two).

Falling and rising

Almost all the native diphthongs of Portuguese are falling: the vowel comes first and the semivowel closes the syllable, as in pai, meu (“my”), dói (“it hurts”). The reverse order — semivowel then vowel, as in quase [ˈkwazɨ] (“almost”) or série [ˈsɛɾjɨ] (“series”) — yields a rising diphthong. These are mostly products of fast speech or of the gu- and qu- clusters; they are not traditionally counted among the basic diphthongs, so the inventory below deals chiefly with the falling ones.

The oral diphthongs

European Portuguese distinguishes a generous set of oral diphthongs, whose quality depends on the base vowel — open or close.

Diphthong	Example	Meaning
[aj]	*pai*	father
[ɐj]	*lei*, *sei*	law; I know
[ɛj]	*papéis*	papers
[oj]	*dois*	two
[ɔj]	*herói*	hero
[uj]	*fui*	I went / was
[aw]	*mau*, *pau*	bad; stick
[ɛw]	*céu*, *chapéu*	sky; hat
[ew]	*meu*, *seu*	my; his/her
[iw]	*viu*, *partiu*	saw; left

Spelling faithfully tracks the quality of the vowel: the acute accent marks the open vowel, setting papéis [pɐˈpɛjʃ] against a close -eis, or herói [ɛˈɾɔj] against boi [ˈboj] (“ox”).

The case of ou and ei

Two “diphthongs” of the spelling are, today, seldom diphthongs in the standard speech of Lisbon. The digraph ou — once [ow] — has been reduced to a plain vowel [o] : ouro (“gold”) and pouco (“little”) are said [ˈoɾu] and [ˈpoku] . And ei is regularly realised as [ɐj] , so that sei sounds [sɐj] , not [sej] .

The nasal diphthongs

Here is one of the most characteristic features of Portuguese. When the base vowel is nasal, the whole diphthong nasalises, the semivowel included. There are four nasal diphthongs, three of them marked in writing by the tilde (til):

Diphthong	Spelling	Example	Meaning
[ɐ̃w̃]	*-ão*, *-am*	*pão*, *cantam*	bread; they sing
[ɐ̃j̃]	*-ãe*, *-ãi*	*mãe*, *pães*	mother; loaves
[õj̃]	*-õe*	*põe*, *lições*	he puts; lessons
[ũj̃]	*-ui*	*muito*	much, very

The diphthong [ũj̃] is a curiosity: it occurs in a single everyday word, muito [ˈmũj̃tu] , and carries no tilde, because its nasality comes from the initial m.

Spelling, plurals and -ão

The ending -ão concentrates much of the language’s difficulty. First, it differs from -am by stress alone, although both are pronounced [ɐ̃w̃] : one writes -ão when the syllable is stressed (cantarão, “they will sing”) and -am when it is unstressed (cantaram, “they sang”). Second, its plural is unpredictable, following three patterns inherited from different Latin etymons:

• -ãos — mão → mãos (“hand → hands”), cidadão → cidadãos (“citizen(s)”);
• -ães — pão → pães (“loaf → loaves”), cão → cães (“dog → dogs”), alemão → alemães (“German(s)”);
• -ões — lição → lições (“lesson → lessons”), coração → corações (“heart → hearts”), the most productive pattern.

Diphthong or hiatus?

Telling a diphthong from a hiatus is decisive for syllabification and for stress. The written sequence may be identical, but only the hiatus splits the vowels across separate syllables — and that difference can itself be marked with an accent, as in saúde [sɐˈudɨ] (“health”, a hiatus, sa-ú-de) against causa [ˈkawzɐ] (“cause”, a diphthong). This is why the study of diphthongs properly comes before the rules of syllable division and written accentuation.