Diphthongs
In general, each Portuguese letter maintains its original pronunciation, i.e. there’s no diphthong that sounds totally different from the separated letters. An 'e' plus an 'u' will always have the sound of an 'e' and an 'u' combined, there will never be any drastic modify in pronunciation.
A diphthong is formed of one vowel that is pronounced stronger (the vowel itself) and one that is pronounced weaker (identified semivowel). The vowels are pronounced as they are one faintly and the other strongly. The letters 'a',' 'e' and 'o' regularly work as vowels, and 'i' and 'u' regularly work as semivowels. A diphthong has to have two vowels at the same syllable. For its pronunciation there’s no rigorous rule.
Differentiate between true diphthongs and adjacent vowels in hiatus are important. For example, in the word saio / /, the i makes a diphthong with the previous vowel, but in saiu, / / or / /, it makes a diphthong with the next vowel. As in Spanish, a hiatus may be selected with an acute accent, distinguishing homographs such as saia / / and saía, / / or / /.
| Oral Diphthongs |
Grapheme |
Pronunciation |
Grapheme |
Pronunciation |
ai, ái |
/ai ~  i1/ |
au, áu |
/au/ |
ei, êi |
/ei ~ i2/ |
eu, êu |
/eu/ |
éi |
/ i ~ i2/ |
éu |
/u/ |
oi |
/oi/ |
ou |
/ou ~ o/ |
ói |
/ i/ |
- |
ui |
/ui/ |
iu |
/iu/ |
| Nasal Diphthongs |
Grapheme |
Pronunciation |
Grapheme |
Pronunciation |
ãe, ãi |
/̃ĩ/ |
ão |
/̃ũ/ |
õe |
/õĩ/ |
- |
1 When followed by a vowel before the stressed syllable, in central Portugal.
2 In central Portugal.
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