The diaeresis[a] (/ - -/, dy-ERR-ə-sis, -EER-; is a diacritical mark used to indicate the separation of two distinct vowels in adjacent syllables when an instance of diaeresis (or hiatus) occurs, so as to distinguish from a digraph or diphthong.
It consists of two dotsplaced over a letter, generally a vowel; when that letter is an ⟨i⟩, the diacritic replaces the tittle: ⟨ï⟩.
The diaeresis diacritic indicates that two adjoining letters that would normally form a digraph and be pronounced as one sound, are instead to be read as separate vowels in two syllables. For example, in the spelling "coöperate", the diaeresis reminds the reader that the word has four syllables co-op-er-ate, not three, *coop-er-ate. In British English this usage has been considered obsolete for many years, and in US English, although it persisted for longer, it is now considered archaic as well. Nevertheless, it is still used by the US magazine The New Yorker. In English language texts it is perhaps most familiar in the spellings naïve, Noël, and Chloë, and is also used officially in the name of the island Teän. Languages such as Dutch, Afrikaans, Catalan, French, Galician, and Spanish make regular use of the diaeresis.
The word diaeresis is from Greek diaíresis (διαίρεσις), meaning "division", "separation", or "distinction". The word trema (French: tréma), used in linguistics and also classical scholarship, is from the Greek trē̂ma (τρῆμα) and means a "perforation", "orifice", or "pip" (as on dice), thus describing the form of the diacritic rather than its function.
In Greek, two dots, called a trema, were used in the Hellenistic period on the letters ι and υ, most often at the beginning of a word, as in ϊδων, ϋιος, and ϋβριν, to separate them from a preceding vowel, as writing was scriptio continua, where spacing was not yet used as a word divider.[b] However, it was also used to indicate that a vowel formed its own syllable (in phonological hiatus), as in ηϋ and Αϊδι.
The diaeresis was borrowed for this purpose in several languages of western and southern Europe, among them Occitan, Catalan, French, Dutch, Welsh, and (rarely) English. As a further extension, some languages began to use a diaeresis whenever a vowel letter was to be pronounced separately. This included vowels that would otherwise form digraphs with consonants or simply be silent. For example, in the orthographies of Spanish, Catalan, French, Galician and Occitan, the graphemes gu and qu normally represent a single sound, [ɡ] or [k], before the front vowels e and i (or before nearly all vowels in Occitan). In the few exceptions where the u is pronounced, a diaeresis is added to it.
This has been extended to Ganda, where a diaeresis separates y from n: anya [aɲa], anÿa [aɲja].
'Ÿ' is sometimes used in transcribed Greek, where it represents the Greek letter υ (upsilon) in hiatus with α. For example, it can be seen in the transcription Artaÿctes of the Persian name Ἀρταΰκτης (Artaüktēs) at the very end of Herodotus, or the name of Mount Taÿgetus on the southern Peloponnesus peninsula, which in modern Greek is spelled Ταΰγετος.
In Catalan, the digraphs ai, ei, oi, au, eu, and iu are normally read as diphthongs. To indicate exceptions to this rule (hiatus), a diaeresis mark is placed on the second vowel: without this the words raïm [rəˈim] ("grape") and diürn [diˈurn] ("diurnal") would be read *[ˈrajm] and *[ˈdiwrn], respectively. The Occitan use of diaeresis is very similar to that of Catalan: ai, ei, oi, au, eu, ou are diphthongs consisting of one syllable but aï, eï, oï, aü, eü, oü are groups consisting of two distinct syllables.
In Dutch, spellings such as coëfficiënt are necessary because the digraphs oe and ie normally represent the simple vowels [u] and [i], respectively. However, hyphenation is now preferred for compound words so that zeeëend (sea duck) is now spelled zee-eend.
In Modern English, the diaeresis, the grave accent and the acute accent are the only diacritics used apart from loanwords. It may be used optionally for words that do not have a morphological break at the diaeresis point, such as "naïve", "Boötes", and "Noël". It is far less commonly used in words such as "coördinate" and "reënter" except in a very few publications – notably The New Yorker and MIT Technology Review under Jason Pontin – and this usage is considered by prescriptive writing guides to be largely archaic. The diaeresis mark is sometimes used in English personal first and last names to indicate that two adjacent vowels should be pronounced separately, rather than as a diphthong. Examples include the given names Chloë and Zoë, which otherwise might be pronounced with a silent e.
In French, some diphthongs that were written with pairs of vowel letters were later reduced to monophthongs, which led to an extension of the value of this diacritic. It often now indicates that the second vowel letter is to be pronounced separately from the first, rather than merge with it into a single sound. For example, the French words maïs [ma.is] and naïve [na.iv] would be pronounced *[mɛ] and *[nɛv], respectively, without the diaeresis mark, since the digraph ai is pronounced [ɛ].[c] The English spelling of Noël meaning "Christmas" (French: Noël [nɔ.ɛl]) comes from this use. Ÿ occurs in French as a variant of ï in a few proper nouns, as in the name of the Parisian suburb of L'Haÿ-les-Roses [la.i le ʁoz] and in the surname of the house of Croÿ [kʁu.i]. In some names, a diaeresis is used to indicate two vowels historically in hiatus, although the second vowel has since fallen silent, as in Saint-Saëns [sɛ̃sɑ̃s] and de Staël [də stal].
The diaeresis is also used in French when a silent e is added to the sequence gu, to show that it is to be pronounced [ɡy] rather than as a digraph for [ɡ]. For example, when the feminine ‑e is added to aigu [eɡy] "sharp", the pronunciation does not change in most accents:[d] aiguë [eɡy] as opposed to the city name Aigues-Mortes [ɛɡ mɔʁt]. Similar is the feminine noun ciguë [siɡy] "hemlock"; compare figue [fiɡ] "fig". In the ongoing French spelling reform of 1990, this was moved to the u (aigüe, cigüe). (In canoë [kanɔ.e] the e is not silent, and so is not affected by the spelling reform.)
In Galician, diaeresis is employed to indicate hiatus in the first and second persons of the plural of the imperfect tense of verbs ended in -aer, -oer, -aír and -oír (saïamos, caïades). This stems from the fact that an unstressed -i- is left between vowels, but constituting its own syllable, which would end with a form identical in writing but different in pronunciation with those of the Present subjunctive (saiamos, caiades), as those have said i forming a diphthong with the following a.
In German, in addition to the pervasive use of umlaut diacritics with vowels, diaeresis above e occurs in a few proper names, such as Ferdinand Piëch and Bernhard Hoëcker.
In Modern Greek, αϊ and οϊ represent the diphthongs /ai̯/ and /oi̯/, and εϊ the disyllabic sequence /e.i/, whereas αι, οι, and ει transcribe the simple vowels /e/, /i/, and /i/. The diacritic can be the only one on a vowel, as in ακαδημαϊκός (akadimaïkós, "academic"), or in combination with an acute accent, as in πρωτεΐνη (proteïni, "protein").
In Portuguese, a diaeresis (Portuguese: trema) was used in (mainly Brazilian) Portuguese until the 1990 Orthographic Agreement. It was used in combinations güe/qüe and güi/qüi, in words like sangüíneo [sɐ̃ˈɡwiniu] "sanguineous". After the implementation of the Orthographic Agreement, it was abolished altogether from all Portuguese words.
Spanish uses the diaeresis obligatorily in words such as cigüeña and pingüino; and optionally in some poetic (or, until 1950, academic) contexts in words like vïuda, and süave.
In Welsh, where the diaeresis appears, it is usually on the stressed vowel, and this is most often on the first of the two adjacent vowels; typical examples are copïo [kɔ.ˈpi.ɔ] (to copy) and mopio [ˈmɔ.pjɔ] (to mop). It is also used on the first of two vowels that would otherwise form a diphthong (crëir [ˈkreː.ɪr] ('created') rather than creir [ˈkrəi̯r] ('believed')) and on the first of three vowels to separate it from a following diphthong: crëwyd is pronounced [ˈkreː.ʊi̯d] rather than [ˈkrɛu̯.ɨd].
...it is much less used than formerly, having been largely replaced by the hyphen...
The special tool we use here at The New Yorker for punching out the two dots that we then center carefully over the second vowel in such words as “naïve” and “Laocoön” will be getting a workout this year, as the Democrats coöperate to reëlect the President.