The diaeresis (also spelled diæresis or dieresis; plural: diaereses) is a diacritical mark consisting of two dots placed over a letter, typically a vowel. Its primary function is to signal that two adjacent vowels belong to separate syllables rather than forming a single digraph or diphthong. The mark is visually identical to the mark used for the German umlaut, but the function and historical origin differ.

Form and names

In English descriptions the term diaeresis is common; in French it is called tréma and in Spanish diéresis. In typographic and digital contexts the sign appears either as a spacing character or as a combining diacritic applied to a base letter. Modern encoding systems provide combined letters (for example, ë and ï) as well as a combining diacritic for flexible composition.

Uses and examples

The diaeresis is used to mark syllable division and indicate that a vowel should be pronounced separately. Examples in names and loanwords include Noël and Chloë. In English it historically appeared in words such as naïve and coöperate to show that the vowels are separate syllables, though many contemporary style guides omit the mark in favor of hyphens or plain spelling.

Other languages employ the mark with distinct roles. In French the tréma signals that a vowel should not form a digraph with the preceding vowel (as in Haïti). Spanish uses a related mark (ü) to show that a u is pronounced in the sequences gue and gui (pingüino). German uses similar-looking dots as umlauts to signal a vowel quality change rather than syllable separation.

History and typographic notes

The word derives from Greek roots meaning "separation" and has been used in classical and medieval orthographies to disambiguate vowel sequences. In modern typography its use varies by language, editorial practice, and font support. Dictionaries and phonetic transcriptions sometimes use the diaeresis to indicate syllabification for learners and readers.

Further reading