Diaeresis
In linguistics, a diaeresis or dieresis (AE) (from Greek diairein, "to divide") is the modification of a syllable by distinctly pronouncing one of its vowels. The diacritic mark composed of two small dots ( ¨ ) placed over a vowel to indicate this modification is also called a diaeresis.
Usage
In French, Greek, and Dutch, and in English borrowings from them, this is often done to indicate that the second of a pair of vowels is to be pronounced as a separate vowel rather than being treated as silent or as part of a diphthong, as in the word naïve or the names Chloë and Zoë. Welsh also uses the accent for this purpose, with the diaeresis usually indicating the stressed vowel. French also uses diaeresis over "i" to indicate syllabification in, for example, Gaëlle and païen. It is called trema or deelteken in Dutch, tréma in French.
The diaeresis is also occasionally used on native English words for the above purposes (as in "coöperate", "reënact", and the surname "Brontë"), but this usage has become very rare since the 1940s. The New Yorker magazine is noted as one of the few sources that still spells "coöperate" with a diaeresis.
In Spanish and Portuguese, it is used over the vowel u to indicate that it is pronounced in places where that vowel would normally be silent. In particular, the u is silent in the letter combinations gue and gui, but in words such as vergüenza ("shame") or pingüino ("penguin"), the u is pronounced, forming a diphthong with the following vowel ([we] and [wi] respectively).
In Catalan, diaereses serve two different purposes. Similarly to Spanish, they are used in the groups güe, güi, qüe, and qüi to indicate that the u is in fact pronounced forming a diphthong with the following vowel ([we] and [wi] respectivelly). For example, aigües ("waters"), qüestió ("matter"). Also, similarly to French, diaereses are used over i or u to indicate that they do not form a diphthong with a preceding vowel. For example, veïna [b@'in@] ("neighbour", feminine), diürn [di'urn] ("diurnal").
Y-diaeresis can also be used in transcribed Greek: there it represents the non-diphthong αυ (alpha upsilon), e.g. in the Persian name Artaÿctes at the very end of Herodotus.
Similar looks, different functions
The similar diacritic mark is used for a different purpose in German: in this language it marks a variation in the pronunciation of vowels known as umlaut. Although sometimes rendered as two vertical or oblique bars above the letter, in most typescripts it is almost indistinguishable from diaeresis — the only difference being that in well-designed typographical fonts umlaut dots will be very close to the letter's body, while diaresis dots will be a bit further up with a bit more of white space between the letter and the dots. In computer screen fonts the difference is usually not noticeable.
The mark evolved from the ligatures æ and œ to a small 'e' written above the letter, simplified to bars or dots; the umlauts, when needed, can be substituted by 'ae', 'oe' and 'ue'; they should not be substituted by the bare vowels 'a', 'o', and 'u'.
The need to distinguish between Umlaut and Trema in Unicode has led to the following recommendation by ISO/IEC JTC 1/SC 2/WG 2:
- To represent Trema use Combining Grapheme Joiner (CGJ, 034F) + Combining Diaeresis (0308)
- To represent Umlaut use Combining Diaeresis (0308)
This should only be applied to cases where the distinction is essential.
Other evolved ligatures
In Finnish, Hungarian and North Germanic languages (i.e., Danish, Icelandic, Norwegian and Swedish) there are characters that appear similar to German umlauts (ü, ä, and ö), and represent sounds similar to the corresponding sounds in German. Despite this, they are in fact considered as letters in their own right, as is å. This is the reason why, unlike in German, it is not correct to replace them with 'ae' or 'oe'. The umlaut, particularly on the letter u, is also used in the transcription of languages that do not use the Roman alphabet, such as Chinese. For example, 女 (meaning "woman") is transcribed as nü.
As such uses do not mark grammatical variation, i.e. of tempus or modus, nor syllable modification, they are not properly cases of umlaut nor of diacritical marking. Hence it ought to be improper to call these characters umlauts; however, there is no better name to use in English.
The Dutch Y, usually written IJ/ij is sometimes written Ÿ/ÿ, but this is not a standard use. If the real IJ/ij characters are not available IJ/ij should be used. Ÿ is used because the "Dutch Y" represents a single letter in all cases, for example IJsselmeer. Note that in Afrikaans (a dialect of/language derived from Dutch) the 'y' does correspond to and is pronounced the same as the Dutch 'ij'.
Other evolved ligatures include the letters W ("double U"), G (originally a modified form of C), and the German ß.
Diaeresis in Cyrillic
Cyrillic letters А, О, У with diaeresis are used in Mari and Keräşen Tatar alphabets for sounds ä, ö, ü since the 19th century. The early Cyrillic alphabet, used to write Old Church Slavonic, also employed diaeresis.
How to produce the characters on computers
Using the ISO-8859-1 character encoding, one can type the letters ä, ë, ï, ö, ü, and ÿ. Dozens more letters with the diaeresis are available in Unicode. Unicode also provides the diaeresis as a combining character U+0308. Characters with umlauts are not encoded, as they are seen as variations of the characters with diaeresis. In those cases where umlauts must be distinguished from diaeresis, the special character U+034F COMBINING GRAPHEME JOINER (CGJ) can be used:
- For diaeresis: X + CGJ + COMBINING DIAERESIS (e.g. a͏̈)
- For umlauts: X + COMBINING DIAERESIS (e.g. ä)
It is then up to the user agent and typeface being used to provide meaningful distinction between the two characters.
Despite the difference between diaeresis and umlauts, the HTML entities for these characters all end in uml; e.g. ä = ä. These entities however use the Unicode diaeresis codepoints when rendered.
TeX also allows double dots to be placed over letters in math mode, using "\ddot{}", or outside of math mode, with the \" control sequence:
However this will give the diaresis-style dots that are too far above the letter's body for good typographical umlauts. TeX's "german" package should be used if possible: it adds the " control sequence (without backslash) which gives nice umlauts.
Time derivatives in mathematics
The derivative with respect to time is often represented as a dot above a variable. Two dots represents the second derivative.
