An oral diphthong is a single syllable in which the tongue glides from one vowel quality to another without passing through a nasal — your mouth moves but the air stays in the mouth, not the nose. Brazilian Portuguese has a rich set of these, and the crucial thing to understand early is that the spelling shows more diphthongs than the mouth actually makes: in everyday speech, several written diphthongs collapse into plain vowels. Getting the gliding ones right — and knowing which ones quietly flatten — is what separates a clear A2 accent from a stiff, over-articulated one.
What counts as a diphthong
A diphthong is two vowel sounds in one syllable: a full vowel plus a glide (a [j] "y" off-glide or a [w] "w" off-glide). Compare this to a hiatus, where two vowels belong to two separate syllables: saída (sa-í-da, "exit") has no diphthong — the accent on the í tells you the i is its own stressed syllable. Knowing the difference matters because Portuguese marks it in the spelling, and reading it wrong throws off your stress and rhythm.
Falling diphthongs (vowel + glide)
These are the common ones. The strong vowel comes first, the glide second. English has all of these sounds, which is good news — your job is mostly to trust them and not to add an extra syllable.
| Spelling | IPA | Example | English anchor |
|---|---|---|---|
| ai | [aj] | pai [paj] | like "pie" |
| ei | [ej] | lei [lej] | like "lay" |
| oi | [oj] | dói [dɔj] / oito [ojtu] | like "boy" |
| ui | [uj] | fui [fuj] | like "phooey" |
| au | [aw] | mau [maw] | like "cow" |
| eu | [ew] | meu [mew] | no clean English match |
| iu | [iw] | viu [viw] | like "ee-w" |
| ou | [o(w)] | sou [so] | like "so" |
Meu pai é mais velho do que a minha mãe.
My dad is older than my mum.
Eu fui ao mercado e vi o que você queria.
I went to the market and saw what you wanted.
Que dia mau! Perdi as chaves de novo.
What a bad day! I lost the keys again.
Notice that eu [ew] has no real English counterpart. English speakers tend to substitute "yoo" or "oh." The trick: start from a clear "eh" and round your lips toward "w" at the very end — eu (I), meu (my), céu (sky).
The big BR simplifications
Here is where Brazilian Portuguese diverges from the spelling, and where most learners over-pronounce.
ou is just [o]
In the vast majority of Brazil, the written diphthong ou is pronounced as a plain closed [o], with no [w] off-glide at all. Sou is [so], not [sow]; falou is [faˈlo], not [faˈlow]; outro is [ˈotɾu]. This is so general that pronouncing a crisp [ow] sounds either bookish or like another language.
Eu sou do Rio, mas moro em São Paulo.
I'm from Rio, but I live in São Paulo.
Ela falou que vem, mas eu não acredito.
She said she's coming, but I don't believe it.
ei reduces to [e] before [ʃ] and [ʒ]
Before a "sh" [ʃ] or "zh" [ʒ] sound, the written ei commonly loses its glide and becomes a plain [e]. Peixe (fish) is typically [ˈpeʃi], queijo (cheese) is [ˈkeʒu], deixa (let/leave) is [ˈdeʃɐ]. The off-glide and the following palatal consonant are made in nearly the same place, so the [j] gets absorbed.
Você quer queijo no pão ou prefere sem?
Do you want cheese on the bread, or would you rather have it without?
Deixa o peixe na geladeira que eu cozinho mais tarde.
Leave the fish in the fridge — I'll cook it later.
This reduction is variable and somewhat regional. Many speakers (notably in parts of the South) keep a fuller [ej]. Both are correct; the monophthongal [e] is the more widespread casual norm.
Other casual losses
In fast speech, ai and ei can flatten in unstressed positions too — caixa (box/cashier) is often [ˈkaʃɐ] rather than a careful [ˈkajʃɐ], by the same logic as peixe. Don't force the glide back in; let it go where natives let it go.
Paga na caixa do lado direito, por favor.
Pay at the till on the right-hand side, please.
Rising diphthongs and glides
In a rising diphthong, the glide comes first and the full vowel second: [j] or [w] + vowel. These show up when an unstressed i or u sits before another vowel: piano can be [ˈpjɐnu], quase [ˈkwazi], água [ˈagwɐ]. The u in qu and gu before a/o is exactly such a [w] glide.
A água já está quase fervendo.
The water's almost boiling.
Ele toca piano desde os seis anos.
He's played the piano since he was six.
Whether a sequence like i + a counts as a rising diphthong (one syllable) or a hiatus (two) depends on the word and the speaker's tempo — in careful speech piano may be three syllables (pi-a-no), in fast speech two. This is a genuine gray area, not a hard rule.
Regional notes
- Carioca (Rio): Because syllable-final S is [ʃ] here, the ei → [e] reduction in words like seis or dezesseis interacts with the strong [ʃ]; expect [sejʃ] ~ [seʃ].
- Sulista (South): Tends to preserve fuller diphthongs, including [ej] before [ʃ]/[ʒ], so peixe may sound more like [ˈpejʃi].
- Nordestino (Northeast): Generally keeps clear, open vowels in diphthongs; the glides are well articulated.
These differences are about how much a diphthong simplifies, never about which vowels are written — so the spelling rules below hold everywhere.
Common Mistakes
English speakers carry over two habits: adding glides where BR has dropped them, and turning Portuguese pure vowels into English-style diphthongs.
❌ sou [sow]
Incorrect — adding an English [w] off-glide to ou
✅ sou [so]
Correct — BR ou is a plain closed [o].
❌ você [voˈsej]
Incorrect — turning final é into an English 'ay' diphthong
✅ você [voˈse]
Correct — it's a pure closed [e], no glide.
❌ pai [paɪ] said as two syllables 'pa-i'
Incorrect — breaking the diphthong into a hiatus
✅ pai [paj]
Correct — one syllable, like English 'pie'.
❌ queijo [ˈkejʒow]
Incorrect — keeping the ei glide and adding a final [w]
✅ queijo [ˈkeʒu]
Correct — ei flattens to [e], final -o raises to [u].
❌ país [pajs]
Incorrect — reading the í as a glide; this means 'parents' (pais)
✅ país [paˈis]
Correct — the accent marks a hiatus: pa-ís, 'country'.
Key Takeaways
- Falling diphthongs (ai, ei, oi, au, eu, iu) are vowel + glide and mostly map onto English sounds — meu [ew] is the one to drill.
- Written ou is plain [o] in BR: sou [so], falou [faˈlo]. Adding [w] is the most common giveaway of a foreign accent.
- Written ei flattens to [e] before [ʃ]/[ʒ]: peixe [ˈpeʃi], queijo [ˈkeʒu].
- An accent on í or ú signals a hiatus (two syllables), not a diphthong: país ≠ pais.
- Don't English-ify pure final vowels — você ends in a clean [e], not "ay."
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- BR Vowel SystemA1 — Brazilian Portuguese has seven oral vowels, not five — because e and o each split into an open and a closed version, a contrast English and Spanish lack.
- Vowel Reduction in BR (Minimal)A2 — How Brazilian Portuguese reduces unstressed vowels — final -e to [i], -o to [u], -a to [ɐ] — and why this is milder than European Portuguese yet triggers the famous t/d palatalization.
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