Until the 20th century, publishing houses and printers in many countries used additional space between sentences. There were exceptions to this traditional spacing method—some printers used spacing between sentences that was no wider than word spacing. This was French spacing—a term synonymous with single-space sentence spacing until the late 20th century. 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. While wide sentence spacing was phased out in the printing industry in the mid-twentieth century, the practice continued on typewriters and later on computers. Perhaps because of this, many modern sources now incorrectly claim that wide spacing was created for the typewriter.
Today the desired or correct sentence spacing is often debated. Many sources now say additional space is not necessary or desirable. From around 1950, single sentence spacing became standard in books, magazines and newspapers. However some sources still state that additional spacing is correct or acceptable. The debate continues, notably on the World Wide Web—as many people use search engines to try to find what is correct. Many people prefer double sentence spacing for informal use because that was how they were taught to type. There is a debate on which convention is more readable, but the few recent direct studies conducted since 2002 have produced inconclusive results.
Widely spaced sentences in typeset text with, at minimum, an em-space between sentences (1909)
Shortly after the invention of movable type, highly variable spacing was created that could create spaces of any size, and allowed for perfectly even justification. 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. These guides—e.g., Jacobi in the UK (1890) and MacKellar, Harpel, and De Vinne (1866–1901) in the U.S.—indicated that sentences should be em-spaced, and that words should be 1/3 or 1/2 em-spaced (illustration right). The relative size of the sentence spacing would vary depending on the size of the word spaces and the justification needs. For most countries, this remained the standard for published work until the 20th century. Yet, even in this period, there were publishing houses (notably in France) that used a standard word space between sentences—a technique called French spacing (illustration below).
Mechanical type and the advent of the typewriter
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. Just as these machines revolutionized the mass production of text, the advent of the typewriter around the same time revolutionized the creation of personal and business documents. But the typewriters' mechanical limitations did not allow variable spacing—typists could only choose the number of times they pressed the space bar. Typists in some English-speaking countries initially learned to insert three spaces between sentences to approximate the wider sentence spacing used in traditional printing, but later settled on two spaces, a practice that continued throughout the 20th century. This became known as English spacing, and marked a divergence from French typists, who continued to use French spacing.
French spaced typeset text (1874)
Transition to single spacing
In the early 20th century, some printers began using one and a half interword spaces (an "en quad") to separate sentences. This standard continued in use into the 1990s.
Magazines, newspapers, and books began to adopt the single space convention in the United States in the 1940s and in the United Kingdom in the 1950s. Typists did not transition to single spacing simultaneously. The average writer still relied on the typewriter to create text—with its inherent mechanical spacing limitations.
Technological advances began affecting sentence spacing methods. In 1941, IBM introduced the Executive, a typewriter capable of proportional spacing—which had been used in professional typesetting for hundreds of years. This innovation broke the hold that the monospaced font had on the typewriter—reducing the severity of its mechanical limitations. By the 1960s, electronic phototypesetting systems ignored runs of white space in text. This was also true of the World Wide Web, as HTML normally ignores additional spacing, although in 2011 the CSS 2.1 standard officially added an option that can preserve additional spaces. In the 1980s desktop publishing software provided the average writer with more advanced formatting tools. By the late 20th century, literature on the written word had begun to adjust its guidance on sentence spacing.
Early positions on typography (the "arrangement and appearance of text") supported traditional spacing techniques in English publications. In 1954, Geoffrey Dowding's book, Finer Points in the Spacing and Arrangement of Type, underscored the widespread shift from a single enlarged em space to a standard word space between sentences.
With the advent of the computer age, typographers began deprecating double spacing, even in monospaced text. In 1989, Desktop Publishing by Design stated that "typesetting requires only one space after periods, question marks, exclamation points, and colons", and identified single sentence spacing as a typographic convention.Stop Stealing Sheep & Find Out How Type Works (1993) and Designing with Type: The Essential Guide to Typography (2006) both indicate that uniform spacing should be used between words, including between sentences.
More recent works on typography weigh in strongly. Ilene Strizver, founder of the Type Studio, says, "Forget about tolerating differences of opinion: typographically speaking, typing two spaces before the start of a new sentence is absolutely, unequivocally wrong." The Complete Manual on Typography (2003) states that "The typewriter tradition of separating sentences with two word spaces after a period has no place in typesetting" and the single space is "standard typographic practice". The Elements of Typographic Style (2004) advocates a single space between sentences, noting that "your typing as well as your typesetting will benefit from unlearning this quaint [double spacing] Victorian habit."
David Jury's book, About Face: Reviving the Rules of Typography (2004)—published in Switzerland—clarifies the contemporary typographic position on sentence spacing:
Word spaces, preceding or following punctuation, should be optically adjusted to appear to be of the same value as a standard word space. If a standard word space is inserted after a full point or a comma, then, optically, this produces a space of up to 50% wider than that of other word spaces within a line of type. This is because these punctuation marks carry space above them, which, when added to the adjacent standard word spaces, combines to create a visually larger space. Some argue that the "additional" space after a comma and full point serves as a "pause signal" for the reader. But this is unnecessary (and visually disruptive) since the pause signal is provided by the punctuation mark itself.
Traditional spacing examples from the 1911 Chicago Manual of Style
Early style guides for typesetting used a wider space between sentences than between words— "traditional spacing," as shown in the illustration to the right. During the 20th century, style guides commonly mandated two spaces between sentences for typewritten manuscripts, which were used prior to professionally typesetting the work. As computer desktop publishing became commonplace, typewritten manuscripts became less relevant and most style guides stopped making distinctions between manuscripts and final typeset products. In the same period, style guides began changing their guidance on sentence spacing. The 1969 edition of the Chicago Manual of Style used em spaces between sentences in its text; by the 2003 edition it had changed to single sentence spacing for both manuscript and print. By the 1980s, the United Kingdom's Hart's Rules (1983) had shifted to single sentence spacing. Other style guides followed suit in the 1990s. Soon after the beginning of the 21st century, the majority of style guides had changed to indicate that only one word space was proper between sentences.
Modern style guides provide standards and guidance for the written language. These works are important to writers since "virtually all professional editors work closely with one of them in editing a manuscript for publication." Late editions of comprehensive style guides, such as the Oxford Style Manual (2003) in the United Kingdom and the Chicago Manual of Style (2010) in the United States, provide standards for a wide variety of writing and design topics, including sentence spacing. The majority of style guides now prescribe the use of a single space after terminal punctuation in final written works and publications. A few style guides allow double sentence spacing for draft work, and the Gregg Reference Manual makes room for double and single sentence spacing based on author preferences. Web design guides do not usually provide guidance on this topic, as "HTML refuses to recognize double spaces altogether." These works themselves follow the current publication standard of single sentence spacing.
The European Union's Interinstitutional Style Guide (2008) indicates that single sentence spacing is to be used in all European Union publications—encompassing 23 languages. For the English language, the European Commission's English Style Guide (2010) states that sentences are always single-spaced. The Style Manual: For Authors, Editors and Printers (2007), first published in 1966 by the Commonwealth Government Printing Office of Australia, stipulates that only one space is used after "sentence-closing punctuation" and that "Programs for word processing and desktop publishing offer more sophisticated, variable spacing, so this practice of double spacing is now avoided because it can create distracting gaps on a page."
National languages not covered by an authoritative language academy typically have multiple style guides—only some of which may discuss sentence spacing. This is the case in the United Kingdom. The Oxford Style Manual (2003) and the Modern Humanities Research Association's MHRA Style Guide (2002) state that only single spacing should be used. In Canada, both the English and French language sections of the Canadian Style, A Guide to Writing and Editing (1997), prescribe single sentence spacing. In the United States, many style guides—such as the Chicago Manual of Style (2003)—allow only single sentence spacing. The most important style guide in Italy, Il Nuovo Manuale di Stile (2009), does not address sentence spacing, but the Guida di Stile Italiano (2010), the official guide for Microsoft translation, tells users to use single sentence spacing "instead of the double spacing used in the United States".
A few reference grammars address sentence spacing, as increased spacing between words is punctuation in itself. Most do not. Grammar guides typically cover terminal punctuation and the proper construction of sentences—but not the spacing between sentences. Moreover, many modern grammar guides are designed for quick reference and refer users to comprehensive style guides for additional matters of writing style. For example, the Pocket Idiot's Guide to Grammar and Punctuation (2005) points users to style guides such as the MLA Style Manual for consistency in formatting work and for all other "editorial concerns". The Grammar Bible (2004) states that "The modern system of English punctuation is by no means simple. 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."
Mignon Fogarty, "Grammar Girl", points out that in the past typewriting used two spaces—in deference to its monospaced font limitations—but "Now that most writing is done on computers it is no longer necessary to type two spaces after a period at the end of a sentence". She answers the question of "How many spaces?" as follows: "On a typewriter, use two. On a computer, use one". This position highlights the late 20th-century transition from the typewriter to the computer, and its effect on sentence spacing.
Today, computers and digital fonts allow sentence spacing variations not possible with the typewriter. Proportional fonts are widely available to average computer users. Computer-based tools such as proportional fonts, kerning, computer-based word processors, and software such as TeX allow users to arrange text in a manner previously only available to professional typesetters.Web browsers eliminate repeated whitespace because of the characteristics of HTML, and as such don't offer the same fine-grained control of spacing as other modern software. Yet, even in the digital age, many school students are still taught to strike the space bar twice between sentences when using computers, contributing to confusion regarding sentence spacing in the 21st century.
The text editing environment in Emacs uses a double space following a period to identify the end of sentences unambiguously; the double space convention prevents confusion with periods within sentences that signify abbreviations. How Emacs recognizes the end of a sentence is controlled by the settings sentence-end-double-space and sentence-end. The vi editor also follows this convention; thus, it is relatively easy to manipulate (jump over, copy, delete) whole sentences in both emacs and vi.
The Unix typesetter program troff uses two spaces to mark the end of a sentence. This allows the typesetter to distinguish sentence endings from abbreviations and to typeset them differently.
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". This subject is still widely debated today.
Many people are opposed to single sentence spacing for various reasons. Some state that the habit of double spacing is too deeply ingrained to change. Others claim that additional space between sentences improves the aesthetics or readability of text. Proponents of double sentence spacing also state that some publishers may still require double spaced manuscript submissions from authors. A key example noted is the screenwriting industry's monospaced standard for screenplay manuscripts, Courier, 12-point font, although some works on screenwriting indicate that Courier is merely preferred - proportional fonts may be used. 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.
One of the most popular arguments against wider sentence spacing is that it was created for monospaced fonts of the typewriter, and is no longer needed with modern proportional fonts. However, proportional fonts existed together with wide sentence spacing for centuries before the typewriter, and remained for decades after its invention. When the typewriter was first introduced, typists were most commonly taught to use three spaces between sentences. This gradually shifted to two spaces, while the print industry remained unchanged in its wide em-spaced sentences. Some sources now state it is acceptable for monospaced fonts to be single spaced today, although other references continue to specify double spacing for monospaced fonts. The double space typewriter convention has been taught in schools in typing classes, and that remains the practice in many cases. Some voice concerns that students will later be forced to relearn how to type.
Most style guides indicate that single sentence spacing is proper for final or published work today, and most publishers require manuscripts to be submitted as they will appear in publication—single sentence spaced. Writing sources typically recommend that prospective authors remove extra spaces before submitting manuscripts, although other sources state that publishers will use software to remove the spaces before final publication.
Claims abound regarding the legibility and readability of the single and double sentence spacing methods—by proponents on both sides. Supporters of single spacing assert that familiarity with the current standard in books, magazines, and the Web enhances readability, that double spacing looks strange in text using proportional fonts, and that the "rivers" and "holes" caused by double spacing impair readability. Proponents of double sentence spacing state that the extra space between sentences enhances readability by providing clearer breaks between sentences and making text appear more legible, particularly noting the very small visual difference between a dot and a comma.
However, typographic opinions are typically anecdotal with no basis in evidence. "Opinions are not always safe guides to legibility of print", and when direct studies are conducted, anecdotal opinions—even those of experts—can turn out to be false. Text that seems legible (visually pleasing at first glance) may be shown to actually impair reading effectiveness when subjected to scientific study.
Direct studies on sentence spacing include those by Loh, Branch, Shewanown, and Ali (2002); Clinton, Branch, Holschuh, and Shewanown (2003); and Ni, Branch, and Chen (2004), with results favoring neither single, double, nor triple spacing. The 2002 study tested participants' reading speed for single and double sentence spaced passages of on-screen text. The authors stated that "the 'double space group' consistently took longer time to finish than the 'single space' group" but concluded that "there was not enough evidence to suggest that a significant difference exists." The 2003 and 2004 studies analyzed on-screen single, double, and triple spacing. In both cases, the authors stated that there was insufficient evidence to draw a conclusion. Ni, Branch, Chen, and Clinton conducted a similar study in 2009 using identical spacing variables. The authors concluded that the "results provided insufficient evidence that time and comprehension differ significantly among different conditions of spacing between sentences".
^In the 1990s, some print and Web sources began referring to double sentence spacing as "French spacing", leading to some ambiguity with the term. See for example, Eckersley et al. 1994. p. 46, and Haley 2006.
^Williams 2003. pp. 13–14. This refers to professionally published works, as it is possible for individual authors to publish works through desktop publishing systems. Williams states, "I guarantee this: never in your life have you read professionally set text printed since 1942 that used two spaces after each period." See also, Felici 2003. p. 81; Strizver 2010; Weiderkehr 2009; Williams 1995. p. 4.
^Lloyd and Hallahan 2009. "During times when many disciplines that recommend the APA's Publication Manual [6th ed., 2009] are advocating evidence-based decisions, it's noteworthy, we think, that these discussions of the rationale for using two spaces at the end of sentences (and after colons) do not appear to be based on scientific examination of the hypothesis that two spaces makes manuscripts more readable."
^Chicago University Press 1911. p. 101. Variable-spaced text (professionally typeset) is unlikely to result in a sentence space exactly twice the size of a word space (which can be seen with a typewriter or monospaced font). Variables such as whether a 1/3 or 1/2 word space is used, and whether the text is justified or unjustified, will vary the difference between a sentence space and word space.
^Felici 2009. Felici illustrates that there are other examples of standard single word spaces used for sentence spacing in this period.
^Adams, et al. 1996. p. 24. Adams, Faux, and Rieber say, "For most composition, the em quad is used to indent the first line of a paragraph, the en quad is used to separate sentences, and the 3-em space is placed between words." An en is half an em and a 3-em space is a third of an em, so the space between sentences would be 1.5 times the space between words.
^For example, the 15th Edition of the Chicago Manual of Style states that "A single character space, not two spaces, should be left after periods at the ends of sentences (both in manuscript and in final, published form) and after colons. University of Chicago Press 2003 Chicago Manual of Style. p. 61.
^University of Chicago Press 1969 Manual of Style (commonly referred to as "Chicago Manual of Style," (1st edition published in 1906.) The 1969 edition of the Manual of Style shows em spacing after sentences in the manuscript example (page 41), but single spacing in the typset example (p. 73).
^Ritter 2003. The 2003 edition of the Oxford Style Manual combined the Oxford Guide to Style (first published as Horace Hart's Rules for Compositors and Readers at the University Press, Oxford in 1893) and the Oxford Dictionary for Writers and Editors (first published as the Authors' and Printers' Dictionary in 1905) Preface.
^University of Chicago Press 2003 Chicago Manual of Style. p. 61. "2.12 A single character space, not two spaces, should be left after periods at the ends of sentences (both in manuscript and in final, published form)." p. 243. "6.11 In typeset matter, one space, not two (in other words, a regular word space), follows any mark of punctuation that ends a sentence, whether a period, a colon, a question mark, an exclamation point, or closing quotation marks." p. 243. "6.13 A period marks the end of a declarative or an imperative sentence. It is followed by a single space."
^Lesina 2009. (1st edition published in 1986.) "Prefazione: Il manuala intende fornire una serie di indicazioni utili per la stesura di testi di carattere non inventive, quali per esempio manuali, saggi, monografie, relazioni professionali, tesi di laurea, articoli per riviste, ecc." (Trans: "[S]tyle manual for academic papers, monographs, professional correspondence, theses, articles, etc.) Preface; Carrada 2010. "Roberto Lesina, Il nuovo manuale di stile, Zanichelli 2009. L'unico vero manuale di stile italiano, di cui nessun redattore può fare a meno". (Trans: "The only real Italian style guide, a must-have for any writer".) The 2009 edition is itself single sentence spaced.
^Microsoft 2010. p. 4.1.8. "Assicurarsi ad esempio che tra la fine e l'inizio di due periodi separati da un punto venga usato un unico spazio prima della frase successiva, invece dei due spazi del testo americano ... A differenza di altre lingue, non va inserito nessuno spazio prima dei segni di punteggiatura." (Trans."Make sure that between two sentences separated by a period a single space is used before the second sentence, instead of the double spacing used in the United States ... Contrary to other languages, no space is to be added before punctuation marks.")
^Bringhurst 2004. p. 30. Bringhurst implies that additional spacing after terminal punctuation is redundant when combined with a period, question mark, or exclamation point. Other sources indicate that the function of terminal punctuation is to mark the end of a sentence and additional measures to perform the same measures are unnecessary.
^Fogarty 2009. p. 78. Other grammar guides recommend one space for computer users. Some indicate that monospaced text could be double spaced in view of the typewriter tradition. See Lutz and Stevenson 2005. pp. 200–202. The Writing Digest Grammar Desk Reference (2005) indicates that "On typed pages, two blank spaces traditionally follow a sentence-ending period", but that "Many editors ... now prefer only a single space" after terminal punctuation. The Blue Book of Grammar and Punctuation (2009) echoes this opinion in that computer users should "use only one space", and with "some typewriters and word processors, [users should] follow ending punctuation with two spaces when using fixed-pitch fonts". See also Straus 2009. p. 52.
^Trotter 1998. p. 112. Trottier refers to Courier as the industry "standard".
^Russin and Downs 2003. p. 17. The authors state that "Courier 12-point is preferred, although New York, Bookman, and Times will do". Allen 2001Moira Anderson Allen suggests that publishers are more interested in readable fonts as opposed to maintaining a fixed-width font standard.
^Tinker 1963. pp. 50, 108, 128. A useful example is the Helvetica font, an ubiquitous font that is considered to be visually pleasing in the construction and viewing of its characters, but has been found to impair reading effectiveness (readability). See Squire 2006. p. 36.
^Clinton 2003. The study did not find "statistically significant differences between reading time of single and double space[d] passages".
^Ni et al. 2009. pp. 383, 387, 390. This study "explored the effects of spacing after the period on on-screen reading tasks through two dependent variables, reading time and reading comprehension".
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