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WIKIPEDIA
Sentence spacing is the horizontal space between sentences in typeset text. It is a matter of typographical convention.[1] Since the introduction of movable-type printing in Europe, various sentence spacing conventions have been used in languages with a Latin-derived alphabet.[2] These include a normal word space (as between the words in a sentence), a single enlarged space, two full spaces, and, most recently in digital media, no space.[3] Although modern digital fonts can automatically adjust a single word space to create visually pleasing and consistent spacing following terminal punctuation,[4] most debate is about whether to strike a keyboard's spacebar once or twice between sentences.[5]
Until the 20th century, publishing houses and printers in many countries used single, but enlarged, spaces between sentences.[6] There were exceptions to this traditional spacing method—printers in some countries preferred single spacing.[7] This was French spacing—a term synonymous with single space sentence spacing until the late 20th century.[8] Double spacing,[9] or placing two spaces between sentences (sometimes referred to as English spacing), came into widespread use with the introduction of the typewriter in the late 19th century.[10] It was felt that with the monospaced font used by a typewriter, "a single word space ... was not wide enough to create a sufficient space between sentences"[11] and that extra space might help signal the end of a sentence.[12] This caused a widespread change in practice. From the late 19th century, printers were told to ignore their typesetting manuals in favor of typewriter spacing; Monotype and Linotype operators used double sentence spacing[12] and this was widely taught in typing classes.[13]
With the introduction of proportional fonts in computers, double sentence spacing became obsolete, according to many experts.[14] These proportional fonts now assign appropriate horizontal space to each character (including punctuation marks), and typesetting programs such as TeX[15] can modify kerning values to adjust spaces following terminal punctuation, so there is less need to increase spacing manually between sentences.[11] From around 1950, single sentence spacing became standard in books, magazines and newspapers.[16] Regardless, many still believe that double spaces are correct. The debate continues,[5] notably on the World Wide Web—as many people use search engines to try to find what is correct.[17] Many people prefer double sentence spacing for informal use because that was how they were taught to type.[18] There is a debate on which convention is more readable, but the few recent direct studies conducted since 2002 have produced inconclusive results.[19]