Portuguese has a generous set of oral diphthongs — syllables that begin with a vowel and glide smoothly into a semivowel without any consonantal break. Most of them are straightforward for learners: pai sounds like English "pie", dois sounds like English "doyce". A few, however, hold traps that only make sense once you understand the Lisbon dialect. The most famous is ou: although written as a diphthong, in standard European Portuguese it is pronounced as a single vowel [o]. Another is ei, which in Lisbon has a noticeably lower, schwa-flavoured nucleus than it does in Brazil. This page covers the seven productive oral diphthongs, their Lisbon realizations, the word-ending patterns that generate them, and the mistakes you are likely to import from English or Spanish.
The seven oral diphthongs
Seven diphthongs are productive in modern European Portuguese. Each combines a vocalic nucleus with a front glide [j] (written i) or a back glide [w] (written u).
| Spelling | IPA (Lisbon) | Rough English equivalent | Example | Translation |
|---|---|---|---|---|
| ai | [aj] | "eye", "pie" | pai, mais, cais | father, more, quay |
| au | [aw] | "ow", "cow" | pau, causa, mau | stick, cause, bad |
| ei | [ɐj] (Lisbon) / [ej] (elsewhere) | close to "uy" in "buy" with a schwa flavour | feira, rei, peito | market, king, chest |
| eu | [ew] | no English match; glide from "eh" to "oo" | meu, seu, euro | my, your, euro |
| oi | [oj] | "boy", "toy" | coisa, boi, noite | thing, ox, night |
| ou | [o] (Lisbon) / [ow] (north) | pure "oh", no glide in Lisbon | pouco, outro, ouço | little, other, I hear |
| iu | [iw] | "ee-oo" glided | partiu, viu, caiu | left, saw, fell |
| ui | [uj] | "oo-ee" glided | fui, azuis, cuidar | I went, blue (pl.), to care for |
O meu pai trabalha no cais todos os dias.
My father works on the quay every day. (pai [paj], cais [kajʃ])
Causaste um grande susto à minha mãe.
You gave my mother a big fright. (causaste [kawˈzaʃtɨ])
Vamos à feira no próximo domingo de manhã.
We're going to the market next Sunday morning. (feira [ˈfɐjɾɐ] — note the Lisbon [ɐj])
O meu euro caiu no chão entre as pedras da calçada.
My euro fell on the ground between the paving stones. (euro [ˈewɾu], caiu [kɐˈiw])
ai and au — the predictable pair
These two are the easiest for English speakers because the closest English equivalents are nearly identical. Ai [aj] is the vowel of English pie, and au [aw] is the vowel of English cow. Both begin with a fully open [a] and glide upward — [aj] to the front, [aw] to the back.
Sai de casa às sete da manhã e volta depois das oito da noite.
He leaves the house at seven in the morning and comes back after eight at night. (sai [saj])
O mau tempo estragou os planos para o piquenique.
The bad weather ruined the plans for the picnic. (mau [maw])
Mais cedo ou mais tarde, vais descobrir a verdade.
Sooner or later, you'll find out the truth. (mais [majʃ])
Be careful with word-final -s: in Lisbon, mais is [majʃ] (with the characteristic coda [ʃ]), not [majs]. The diphthong itself is the same; only the closing fricative changes.
ei — the Lisbon surprise
Of all the diphthongs, ei is the one where European and Brazilian pronunciation most visibly diverge. Brazilian speakers say [ej], close to English day without the final [j]-like fade. Standard Lisbon speakers lower the nucleus: [ɐj], roughly "uh-ee" run together. This lowering is one of the auditory hallmarks of the Lisbon dialect — not universal across Portugal (central and northern regions may use [ej]), but the reference for learners.
Sei que te aconteceu alguma coisa ontem, mas não sei o quê.
I know something happened to you yesterday, but I don't know what. (sei [sɐj] in Lisbon)
A feira do livro começa no dia três.
The book fair begins on the third. (feira [ˈfɐjɾɐ])
O peixe ficou caro este ano.
Fish has become expensive this year. (peixe [ˈpɐjʃɨ])
Primeiro a chuva, depois o sol — o tempo está confuso.
First the rain, then the sun — the weather is confusing. (primeiro [pɾiˈmɐjɾu])
In rapid Lisbon speech, the [ɐj] can compress further toward [ɐ], especially in very unstressed position, but the schwa-flavoured nucleus is the defining feature. If you have trained on Brazilian recordings and you switch to Lisbon materials, the change from [ej] to [ɐj] will be the first thing your ear notices.
eu — no English equivalent
The diphthong eu [ew] has no close match in English. It begins at the close-mid [e] — the same vowel as in ê — and glides toward [u], the tight back vowel. English eh-oo said quickly is the closest approximation, but the [e] nucleus must be pure (no English [ɛj] diphthongization) and the glide must land cleanly on [u], not on [ʊ] or [ə].
O meu irmão mais novo chama-se Eduardo.
My younger brother is called Eduardo. (meu [mew])
Ela deu-me um abraço e foi embora.
She gave me a hug and left. (deu [dew])
O Euro foi introduzido em 2002.
The Euro was introduced in 2002. (Euro [ˈewɾu])
Prefiro o teu bolo ao meu.
I prefer your cake to mine. (teu [tew], meu [mew])
The contrast between [e] nucleus and [ɛ] nucleus matters: véu [vɛw] "veil" is a different word from a hypothetical *veu with closed [e]. In this case the spelling — acute on é — tells you clearly which quality to use.
oi — the clear one
The diphthong oi [oj] is close to English oy in boy, though the Portuguese [o] nucleus is purer — no opening glide as in English. The result is a clean, almost French-sounding diphthong.
Comprei uma coisa muito gira no mercado.
I bought something really nice at the market. (coisa [ˈkojzɐ])
Boa noite, até amanhã.
Good night, see you tomorrow. (noite [ˈnojtɨ])
Dois cafés, por favor.
Two coffees, please. (dois [dojʃ])
Note the distinction between oi [oj] and ói [ɔj]. The open-ó variant appears in a few words: herói [iˈɾɔj] "hero", constrói [kõʃˈtɾɔj] "builds". The acute accent tells you the nucleus is open.
O herói do filme constrói uma nova vida depois da guerra.
The film's hero builds a new life after the war. (herói [iˈɾɔj], constrói [kõʃˈtɾɔj])
ou — the Lisbon monophthong
This is where the spelling lies. Written ou looks like it should be [ow], and in the north of Portugal (around Porto and Braga) it often is. In the standard Lisbon dialect, however, ou has monophthongized — it has merged to a single pure [o]. There is no glide. Pouco is [ˈpoku], not [ˈpowku]. Outro is [ˈotɾu], not [ˈowtɾu]. Ouço is [ˈosu], not [ˈowsu].
Pouco a pouco, vou aprendendo a falar melhor.
Little by little, I'm learning to speak better. (pouco [ˈpoku], vou [vo])
Ouço música enquanto trabalho.
I listen to music while I work. (ouço [ˈosu])
Outro dia encontrei-o no supermercado.
The other day I ran into him at the supermarket. (outro [ˈotɾu])
Vou-me embora, já é tarde.
I'm leaving, it's already late. (vou [vo])
The result is that ou and ô are often homophones in Lisbon: ouve "hears" and ove would sound the same (ove doesn't exist, but the principle shows why spelling reform hasn't collapsed ou to ô — the historical distinction is preserved in orthography even though pronunciation has merged).
Why ou became [o]
Historically, Latin -au- and Latin -ō- gave Old Portuguese the diphthong [ow], preserved in spelling. In the Lisbon standard, that diphthong monophthongized over several centuries — a sound change paralleled in some other Ibero-Romance varieties. The north of Portugal preserves the older [ow], and that pronunciation is not "wrong" — it is a regional variant. But for learners aiming at the coastal standard, [o] is the target.
iu and ui — the mirrored pair
The diphthongs iu [iw] and ui [uj] are mirror images. Both have a high-vowel nucleus and a glide toward the opposite high vowel.
Iu [iw] appears in many third-person preterite forms of -ir verbs: partiu "left", viu "saw", saiu "left", caiu "fell", sentiu "felt", vestiu "dressed". It is overwhelmingly a verb-morphology diphthong — nearly every -iu you encounter will be a preterite.
O comboio partiu antes de eu chegar à estação.
The train left before I got to the station. (partiu [pɐɾˈtiw])
Ela viu-te na rua ontem à tarde.
She saw you on the street yesterday afternoon. (viu [viw])
Ui [uj] appears in fui "I went/was", azuis "blue (pl.)", cuidar "to care for", and the critical exception muito (which is nasal — see the nasal diphthongs page).
Fui ao cinema com a minha irmã ontem.
I went to the cinema with my sister yesterday. (fui [fuj])
Os meus olhos são azuis e os dela são castanhos.
My eyes are blue and hers are brown. (azuis [ɐˈzujʃ])
Word-ending patterns that generate diphthongs
Many Portuguese diphthongs appear predictably in plural and derivational morphology. Knowing the patterns helps you read new words at sight.
| Ending | Pattern | Examples |
|---|---|---|
| -ais | plural of nouns/adjectives in -al | animais, cardinais, jornais, hospitais |
| -eis | plural of nouns/adjectives in -el | papéis, hotéis, pincéis, anéis |
| -óis | plural of nouns/adjectives in -ol | heróis, espanhóis, lençóis, anzóis |
| -uis | plural of nouns/adjectives in -ul | azuis, paúis |
| -iu | 3rd-person preterite of -ir verbs | partiu, saiu, vestiu, sentiu |
| -ou | 3rd-person preterite of -ar verbs (written -ou, said [o] in Lisbon) | falou, chegou, trabalhou, comprou |
Os animais do jardim zoológico estão cada vez mais protegidos.
The animals at the zoo are increasingly protected. (animais [ɐniˈmajʃ])
Precisamos de papéis novos para a impressora.
We need fresh paper for the printer. (papéis [pɐˈpɛjʃ])
Os heróis nacionais estão homenageados no panteão.
The national heroes are honoured in the pantheon. (heróis [iˈɾɔjʃ])
Ela falou comigo por mais de uma hora.
She talked to me for over an hour. (falou [fɐˈlo] in Lisbon)
Notice that the -ou ending of -ar preterite verbs is pronounced [o] in Lisbon — not [ow]. This is one of the most frequent Lisbon markers in everyday conversation; every time someone tells you what happened yesterday, they will use -ou forms, and you will hear pure [o].
Production tips — keeping glides clean
Three production reminders cover most of the work.
Keep the glide short and high. Portuguese glides end on a tight [j] or [w]. Don't let the glide wander into [ɪ] or [ʊ] (the English lax versions). The second element of pai should be a tight [j], just like the y in English yes produced very quickly.
Don't insert a glide where there isn't one. English speakers instinctively add [j] to any final [e] and [w] to any final [o]. In Portuguese, pure [o] and [e] stay pure. Café is [kɐˈfɛ], not [kɐˈfɛj]. Pouco is [ˈpoku] in Lisbon, not [ˈpowku].
Preserve the nucleus quality. If the diphthong is written with an acute accent (-éis, -óis), the nucleus is the open vowel [ɛ] or [ɔ]. If written plain (-eis, -ois), the nucleus may be closed [e] or [o]. Accent marks do the same work in diphthongs that they do in monophthongs.
Os hotéis do centro estão todos cheios este fim de semana.
The downtown hotels are all full this weekend. (hotéis [oˈtɛjʃ] — open ɛ)
Ouço sempre rádio de manhã enquanto bebo o café.
I always listen to the radio in the morning while I have my coffee. (ouço [ˈosu], café [kɐˈfɛ])
Comparison with English and Spanish
English has its own diphthong inventory (eye, cow, boy, buoy, oh, ay), but the glides often lax into [ə]-flavoured offglides — listen to how English speakers end oh with a slight schwa. Portuguese glides are tight and high, without this laxing. English also lacks [ew] (the eu diphthong), which has to be learned from scratch.
Spanish has a similar set of diphthongs (ai, ei, oi, au, eu), and Spanish speakers import most of them unchanged. The trouble spots are ei (Spanish [ej] vs. Lisbon [ɐj]) and ou (Spanish [ow] vs. Lisbon [o]). Spanish speakers also often replace [ʒ] or [ʃ] around diphthongs with their own [s], missing the voicing contrasts of Lisbon codas.
Em espanhol, "causa" é [ˈkawsa]; em português, "causa" é [ˈkawzɐ], com um z.
In Spanish, 'causa' is [ˈkawsa]; in Portuguese, 'causa' is [ˈkawzɐ], with a z.
Common Mistakes
Mistake 1: Pronouncing ou as [ow]
The textbook trap. Every Brazilian course reinforces [ow], but standard Lisbon has [o]. If you want to sound European rather than Brazilian, this single change does a lot of work.
❌ Saying *pouco* as [ˈpowku].
Brazilian. In Lisbon: [ˈpoku], no glide.
✅ Saying *pouco* as [ˈpoku].
Pure [o], no glide — the Lisbon standard.
Mistake 2: Using [ej] for ei instead of Lisbon's [ɐj]
A quieter marker, but still distinct. Lisbon speakers lower the nucleus to [ɐ].
❌ Saying *feira* as [ˈfejɾɐ].
Northern or Brazilian. Lisbon is [ˈfɐjɾɐ].
✅ Saying *feira* as [ˈfɐjɾɐ].
The Lisbon lowering of the ei nucleus.
Mistake 3: Splitting a diphthong into two syllables
Learners sometimes insert a hiatus where the native speaker has a single gliding syllable. Pai is one syllable, not two; pouco is two syllables, not three.
❌ Saying *pai* as [ˈpa.i].
Two syllables with hiatus. It's one syllable: [paj].
✅ Saying *pai* as [paj].
One gliding syllable.
Mistake 4: Adding a glide where Portuguese has a pure vowel
The reverse error. After [o] or [e], English speakers reflexively add [w] or [j]. In Portuguese, final -ó, -ô, -é, and -ê are pure.
❌ Saying *café* as [kɐˈfɛj].
English-style glide. It's [kɐˈfɛ], pure open e.
✅ Saying *café* as [kɐˈfɛ].
No glide.
Mistake 5: Missing the open vs. closed nucleus in -éis vs. -eis
An acute on the é tells you the nucleus is open [ɛ]. Without the accent, the nucleus is closed [e]. Papéis [pɐˈpɛjʃ] is different from a hypothetical papeis that doesn't exist — but the pattern extends to other words where spelling matters.
❌ Saying *hotéis* as [oˈtejʃ].
Ignores the acute accent. It's [oˈtɛjʃ] with open ɛ.
✅ Saying *hotéis* as [oˈtɛjʃ].
Open ɛ nucleus as marked by the acute.
Mistake 6: Pronouncing verb endings in -ou as [ow]
Every -ar verb's third-person preterite ends in -ou. Falou, chegou, comprou, trabalhou — all of them [o] in Lisbon, never [ow]. This one correction instantly makes your past tense sound European.
❌ Saying *chegou* as [ʃɨˈɡow].
Brazilian. Lisbon: [ʃɨˈɡo].
✅ Saying *chegou* as [ʃɨˈɡo].
Pure [o].
Key Takeaways
- European Portuguese has seven productive oral diphthongs: ai [aj], au [aw], ei [ɐj], eu [ew], oi [oj], ou [o], iu [iw], ui [uj].
- All Portuguese diphthongs are closing — the tongue moves from open/mid to close, ending in a glide.
- The Lisbon ei has a lowered nucleus [ɐj], contrasting with Brazilian [ej] and northern Portuguese [ej]. This is a defining auditory marker.
- The Lisbon ou is monophthongized to [o]. Despite the two-letter spelling, there is no glide in Lisbon speech — pouco is [ˈpoku], falou is [fɐˈlo].
- Distinguish open from closed nuclei in diphthongs: -éis is [ɛj], -eis would be [ej]; -óis is [ɔj], -ois is [oj]. The acute accent tells you the open variant.
- The word muito is nasal, not oral — see the nasal diphthongs page for the ũj exception.
- Plural patterns generate predictable diphthongs: -al → -ais, -el → -eis/-éis, -ol → -ois/-óis, -ul → -uis.
- Verb morphology generates others: -ar preterites in -ou, -ir preterites in -iu.
- Spanish speakers need to lower ei and monophthongize ou; English speakers must keep glides tight and avoid inserting glides where none exist.
Related Topics
- Nasal DiphthongsA2 — The four nasal diphthongs of European Portuguese — ão, ãe, õe, and the lone nasal ui of muito — how to recognize them, how to produce them, and how to handle the three plural patterns of -ão nouns.
- The Portuguese Vowel SystemA1 — A guide to the nine oral vowels of European Portuguese — open and closed mid-vowels, stressed vs. unstressed quality, the reduced vowels that dominate the dialect, and how the spelling encodes it all.
- Vowel Reduction in European PortugueseA1 — The single most distinctive feature of European Portuguese — how unstressed vowels are weakened, centralized, or deleted, producing the compressed, consonant-rich texture of the Lisbon standard.
- European Portuguese Pronunciation OverviewA1 — A tour of the sound system of European Portuguese — the vowels, the consonants, the stress patterns, and the features that give the Lisbon standard its unmistakable compressed, consonant-rich character.
- European vs Brazilian PronunciationA2 — A systematic side-by-side comparison of the two major Portuguese varieties — vowel reduction, syllable-final s, coda l, rhotics, palatalization, diphthongs, and intonation — with examples for each contrast.