Ligature (typography)

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In writing and typography, a ligature occurs where two or more letterforms are written or printed as a unit. Generally, ligatures replace characters that occur next to each other when they share common components. Ligatures are a subset of a more general class of figures called "contextual forms". Contextual forms describe the case where the particular shape of a letter depends on its context (surrounding letters, whether or not it's at the end of a line, etc.).

One of the most common ligatures is "fi." Since the dot above a lowercase "I" interferes with the loop on the lowercase "F," when "f" and "i" are printed next to each other, they are combined into a single figure with the dot absorbed into the "f," which appears as "ﬁ". Perhaps the most common ligature is the ampersand &: this was originally a ligature of 'Et', Latin for 'and'.

The letter W is not in the Latin alphabet, and the sound was originally written in various ways, among them the Runic letter Wynn (Ƿ), and with two Vs or Us written together. VV developed into W, but the modern Latin letter W is not a true ligature, as it represents a different sound than VV/UU.

An example of a more general contextual form is the Greek lowercase sigma. When typesetting Greek, the selection of which sigma to use is determined by whether or not the letter occurs at the end of the word.

Ligatures were originally used by medieval scribes to conserve space and increase writing speed. A 14th century manuscript, for example, will include hundreds of ligatures. Early typefaces used ligatures in order to emulate the appearance of hand-lettered manuscripts. As typesetting became more automated, most of these ligatures fell out of common use. It is only recently that computer based typesetting has encouraged people to start using them again (although "fine art" printers have used them all along). Generally, ligatures work best in typefaces which are derived from calligraphic letterforms. Also useful are contextual forms, such as swash capitals, terminal characters, and so on.

Ligatures are not limited to Latin script. Some forms of the Glagolitic script, used from Middle ages to the 19th century to write some Slavic languages, have a "boxy" shape that leads to a more frequent use of ligatures. And in the Arabic alphabet, which has a very "fluid" shape, there is usually ligature between every single letter.

Typical ligatures in Latin script

TeX is an example of a computer typesetting system that makes use of ligatures automatically. The Computer Modern Roman typeface, which is provided with TeX, includes the five common ligatures ff, fi, fl, ffi, and ffl. When TeX finds these letters juxtaposed in the text, it substitutes the appropriate ligature (unless overridden by the typesetter). Some believe that the writer should be able to decide whether to use a ligature or not; others that it is the job of a typesetter.

This table shows unligatured sets of letters on the left, the corresponding Unicode ligature in the middle column, and the Unicode code points on the right. Provided you are using an operating system and user agent that can handle Unicode, and have the correct Unicode fonts installed, some or all of these will display correctly. See also the provided graphic.

	Ligature	Unicode
AE	Æ	198
ae	æ	230
OE	Œ	0338
oe	œ	0339
ff	ﬀ	64256
fi	ﬁ	64257
fl	ﬂ	64258
ffi	ﬃ	64259
ffl	ﬄ	64260
ij	ĳ	0307
ſt	ﬅ	64261
st	ﬆ	64262
ſs (or ſz)	ß	223
Et	&	38

It is important to note that the letter Æ (æ) when used in the Danish, Norwegian languages or Old English is not a typographical ligature, and must never be treated as such. It is a distinct letter and vowel. Likewise, the letter ß is a distinct letter in German, and the letter ĳ is a distinct letter in Dutch.