Middle dot

A middle dot is one of several types of dots that occur in the middle of a character space, such as the examples in the following table. Depending on context, it may serve as a punctuation mark or a diacritic.

Characters in the Symbol column, above, may not render in all browsers.

The dot called interpunct was used regularly in early Latin, but had long been replaced by space. The Georgian language uses · (middot) as a comma. The Taiwanese dot above right (indicating a more open vowel) is often expressed as a Unicode middle dot, as the necessary combining character was not codified prior to June 2004; historically, it was derived in the late 19th century from an older barred-o with curly tail as an adaptation to the typewriter. Bernhard Karlgren used a middle dot to represent the glottal stop in his reconstruction of medieval Chinese. As well, the Greek Ano Teleia (a semicolon-like punctuation mark, lit. "upper dot") is often expressed as a middle dot, although Unicode provides for a unique U+0387. [1]

In Chinese and Japanese, transcribed foreign words, especially names, are separated by the middle dot (・) when necessary. This is because neither Chinese nor Japanese uses space or any punctuation to separate words; in Japanese, the mixture of katakana, kanji, and hiragana gives some indication of word boundary. A middle dot is also sometimes used to separate lists in Japanese instead of the Japanese comma ("、" known as tōten). In Japanese typography, the "katakana middle dot" (as the Unicode consortium calls it) has a fixed width that is the same as most kana characters, known as fullwidth. In Chinese, the middle dot is also fullwidth in printed matter, but the regular middle dot (·) is used in computer input, which is then rendered as fullwidth in Chinese-language fonts. Note that while some fonts may render the Japanese katakana middle dot as a square under great magnification, this is not a defining property of the middle dot that is used in China or Japan.

In Catalan, the punt volat (literally, "flown dot") is used between two l's (thus: l·l) in cases where each belongs to a separate syllable (e.g. col·lecció, collection). This is to distinguish the true "double-l" pronunciation from that of the letter-combination ll (without a dot) which in Catalan stands for the single sound represented by the IPA symbol [λ] (e.g. castellà, Castilian) . In spelling, l·l is called ela geminada ("geminate l") and ll ella. Where a middle dot is unavailable, a period is frequently used: col.lecció. Unicode has unique code points for the letters Ŀ (U+013F) and ŀ (U+0140), but they are not frequently used. Also, in Medieval Catalan the symbol was sometimes used to note certain ellisions, much like the modern apostrophe.

In British publications up to the mid-1970s, especially scientific and mathematical texts, the decimal point was commonly typeset as a middle dot. When the British currency was decimalised in 1971, the official advice issued was to write decimal amounts with a raised point (thus: £21·48) and to use a decimal point "on the line" only when typesetting constraints made it unavoidable. The widespread introduction of electronic typewriters and calculators soon afterwards was probably a major factor contributing to the decline of the raised decimal point, although it can still sometimes be encountered in academic circles: e.g. Cambridge University 2004, and Durham University 2004, and is fairly commonly used by mathematics teachers in schools.

In mathematics, a small middle dot can be used to represent the product, for example x⋅y for the product of x and y. When dealing with scalars, it is interchangeable with the times symbol: x⋅y means the same thing as x×y. However, when dealing with vectors, the dot product is distinct from the cross product. This usage has its own designated code point in Unicode, U+2219 (∙), called the "bullet operator".

In chemistry, the middle dot is used to separate the parts of formulas of addition compounds, mixture salts or solvates (mostly hydrates), such as of copper(II) sulfate pentahydrate, CuSO₄·5H₂O.

In the Shavian alphabet, the middle dot is used before a word to denote it as a proper noun.

See also

• Punctuation