The tilde and nasality

Of all the diacritics of Portuguese, the tilde (~) is the most distinctive of the language. Unlike the acute or the circumflex, it does not mark the stressed syllable or the openness of a vowel: it marks nasality. For this reason it is described precisely not as an accent but as a sign of nasality — the mark that the vowel beneath it is articulated with air passing through the nasal cavity.

Where the tilde comes from

The tilde is an inheritance of medieval writing. When scribes needed to abbreviate a nasal consonant — m or n — they drew a small superscript stroke over the preceding letter, the Latin titulus, from which the word til (tilde) itself derives. That stroke stood for the omitted n (or m): one wrote nõ for non, bõa for bona. When, in the evolution of Galician-Portuguese, the intervocalic Latin nasal consonants fell away, the surviving vowel kept its nasality — and the tilde, once a mere abbreviation, came to record it.

In older spelling the tilde could appear over any vowel — ĩ, ũ, ẽ — and many of those spellings later lost their nasality or were simplified (lũa became lua, bõo became bom). Modern orthography fixed the tilde on just two vowels.

Where the tilde occurs today

In present-day Portuguese the tilde is written exclusively over a and o, giving the letters ã and õ. The vowel ã appears on its own at the end of a word or syllable (lã “wool”, irmã “sister”, manhã “morning”, maçã “apple”); the vowel õ never stands alone — it occurs only in the diphthong õe. Over the other vowels the tilde has no use today.

Spelling	Example	IPA	Meaning
*ã*	*lã*	[lɐ̃]	wool
*ã*	*irmã*	[iɾˈmɐ̃]	sister
*ã*	*manhã*	[mɐˈɲɐ̃]	morning

Two ways of marking nasality

The tilde is not the only resource the orthography has for writing a nasal vowel. There are in fact two systems that coexist:

• the tilde, over a and o, chiefly word-finally: lã, pão, põe;
• the consonants m and n after the vowel, within the same syllable, when the nasal vowel is followed by another sound: campo “field”, canto “corner”, fim “end”, bom “good”, som “sound”, untar “to grease”.

The split between m and n follows a simple, ancient rule: write m before p and b (campo, tempo, embora), and n before the other consonants (canto, onda, infinito). In both cases the consonant is not pronounced as such: it serves only as a graphic cue that the preceding vowel is nasal.

The nasal diphthongs

It is in the nasal diphthongs that the tilde stands out most, for it is the tilde that distinguishes, in writing, a nasal vowel from a true diphthong. Portuguese has three nasal diphthongs spelled with a tilde — ão, ãe and õe — alongside the case of ui in muito “much”, which is nasal but unmarked.

Spelling	Example	IPA	Typical plural
*ão*	*pão*, *mão*, *coração*	[ɐ̃w̃]	*-ãos*, *-ães* or *-ões*
*ãe*	*mãe*, *cães*, *pães*	[ɐ̃j̃]	*-ães*
*õe*	*põe*, *lições*, *leões*	[õj̃]	*-ões*

The diphthong ão is especially productive and has three possible plurals, inherited from distinct Latin endings: mão → mãos “hands”, pão → pães “loaves”, leão → leões “lions”. The word pão “bread” is pronounced [pɐ̃w̃] — a nasal central vowel followed by a likewise nasalised glide.

The tilde is not a stress accent

It bears repeating: the tilde marks nasality, not stress. A word may carry a tilde on one syllable and its stress on another, requiring an additional graphic accent. This is what happens in órgão [ˈɔɾɣɐ̃w̃] “organ”, órfão “orphan”, bênção “blessing” and sótão “attic”: the acute or circumflex marks the stressed syllable, while the tilde merely nasalises the unstressed final one.

This yields a precious orthographic distinction in verb conjugation. The ending -ão, with a tilde, marks the stressed future form (3rd person plural): cantarão “they will sing”, farão “they will do”, serão “they will be”. The ending -am, without a tilde, marks the unstressed forms of the preterite and other tenses: cantaram “they sang”, cantavam “they used to sing”, fizeram “they did”. Both are read with the same final diphthong [ɐ̃w̃] , but only the tilde (and the placement of stress) reveals that in one the last syllable is stressed and in the other it is not.

In short

The tilde compresses a thousand years of the language’s history into a single stroke: it began as the abbreviation of a lost n and became the graphic emblem of Portuguese nasality. Today it lives over a and o, shares with m and n the task of signalling nasal vowels, and draws the diphthongs — ão, ãe, õe — that give Portuguese its unmistakable sound.