Sentence spacing
[3] With the introduction of the typewriter in the late 19th century, typists used two spaces between sentences to mimic the style used by traditional typesetters.
[4] While wide sentence spacing was phased out in the printing industry in the mid-20th century, the practice continued on typewriters[5] and later on computers.
[14] Early American, English, and other European typesetters' style guides (also known as printers' rules) specified spacing standards that were all essentially identical from the 18th century onwards.
[7] Mechanical type systems introduced near the end of the 19th century, such as the Linotype and Monotype machines, allowed for some variable sentence spacing similar to hand composition.
But the typewriters' mechanical limitations did not allow variable spacing—typists could only choose the number of times they pressed the space bar.
[22] In the early 20th century, some printers began using one and a half interword spaces (an "en quad") to separate sentences.
In 1941, IBM introduced the Executive, a typewriter capable of proportional spacing,[26] which had been used in professional typesetting for hundreds of years.
[30] Early positions on typography (the "arrangement and appearance of text")[31] supported traditional spacing techniques in English publications.
[37] During the 20th century, style guides commonly mandated two spaces between sentences for typewritten manuscripts, which were used prior to professionally typesetting the work.
[47] The majority of style guides now prescribe the use of a single space after terminal punctuation in final written works and publications.
[48] Web design guides do not usually provide guidance on this topic, as "HTML refuses to recognize double spaces altogether".
[54] In Canada, both the English- and French-language sections of the Canadian Style, A Guide to Writing and Editing (1997), prescribe single sentence spacing.
Additionally, the Duden, the German-language dictionary most commonly used in Germany,[62] indicates that double sentence spacing is an error.
A book that covers all the bases would need to be of considerable breadth and weight and anyone interested in such a resource is advised to consult the Chicago Manual of Style.
Computer-based word processors and typesetting software such as troff and TeX allow users to arrange text in a manner previously only available to professional typesetters.
Early versions of Troff,[72] which only typeset in fixed-width fonts, would automatically add a second space between sentences, which were detected based on the combination of terminal punctuation and a line feed.
[73] Multiple spaces are eliminated by default in most World Wide Web content, whether or not they are associated with sentences.
[74] James Felici, author of the Complete Manual of Typography, says that the topic of sentence spacing is "the debate that refuses to die … In all my years of writing about type, it's still the question I hear most often, and a search of the web will find threads galore on the subject".
[76] Proponents of double sentence spacing also state that some publishers may still require double-spaced manuscript submissions from authors.
[78] Some reliable sources state simply that writers should follow their particular style guide, but proponents of double spacing caution that publishers' guidance takes precedence, including those that ask for double-sentence-spaced manuscripts.
[80] However, proportional fonts existed together with wide sentence spacing for centuries before the typewriter and remained for decades after its invention.
[86] Claims abound regarding the legibility and readability of the single and double sentence spacing methods—by proponents on both sides.
[89] "Opinions are not always safe guides to legibility of print",[90] and when direct studies are conducted, anecdotal opinions—even those of experts—can turn out to be false.
[91] Text that seems legible (visually pleasing at first glance) may be shown to actually impair reading effectiveness when subjected to scientific study.
[95] The 2002 study tested participants' reading speed for passages of on-screen text with single and double sentence spacing.
[98] A 2018 study of 60 students found that those who used two word spaces between sentences read the same text 3% faster than with a monospaced font (Courier New).
[108] Canadian typographer Geoffrey Dowding suggests possible explanations of this phenomenon:A carefully composed text page appears as an orderly series of strips of black separated by horizontal channels of white space.
Conversely, in a slovenly setting the tendency is for the page to appear as a grey and muddled pattern of isolated spats, this effect being caused by the over-widely separated words.
The eye also tends to be confused by a feeling of vertical emphasis, that is, an up & down movement, induced by the relative isolation of the words & consequent insistence of the ascending and descending letters.
This movement is further emphasized by those "rivers" of white which are the inseparable & ugly accompaniment of all carelessly set text matter.
