Sentence spacing

Traditional typesetting

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. 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.

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.

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, to some extent, 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 move 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.

Typography

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.

Style guides

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".

Language guides

Some languages, such as French and Spanish, have academies that set language rules. Their publications typically address orthography and grammar as opposed to matters of typography. Style guides are less relevant for such languages, as their academies set prescriptive rules. For example, the Académie française publishes the Dictionnaire de l'Académie française for French speakers worldwide. The 1992 edition does not provide guidance on sentence spacing, but is single-sentence-spaced throughout—consistent with historical French spacing. The Spanish language is similar. The most important body within the Association of Spanish Language Academies, the Real Academia Española, publishes the Diccionario de la Lengua Española, which is viewed as prescriptive for the Spanish language worldwide. The 2001 edition does not provide sentence spacing guidance, but is itself single sentence spaced. The German language manual Empfehlungen des Rats für Deutsche Rechtschreibung ("Recommendations of the Council for German Orthography") (2006) does not address sentence spacing. The manual itself uses one space after terminal punctuation. Additionally, the Duden, the German language dictionary most commonly used in Germany, indicates that double sentence spacing is an error.

Grammar guides

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."

Digital age

In the computer era, spacing between sentences is handled in several different ways by various software packages. Some systems accept whatever the user types, while others attempt to alter the spacing, or use the user input as a method of detecting sentences. 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.

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. Early versions of troff, 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.

Microsoft Word does not treat sentences differently by default, but the grammar checking can be set to prefer a specific number of spaces between sentences.

LaTeX typesets an "intersentence space" after a period unless instructed otherwise. This is a variable space that is normally wider than an "interword space".

On some modern touch-screen platforms, including Android and iOS, typing two spaces in a row is automatically interpreted to mean the end of a sentence, and a period is automatically inserted. However, only one space is retained.

Multiple spaces are eliminated by default in most World Wide Web content, regardless of whether they are associated with sentences or not. There are options for preserving spacing, such as the CSS white-space property, and the <pre> tag. Twitter retains extra spaces in user input on their website. HTML also includes several other space entities which are not collapsed, such as an em space, an en space, and a non-breaking space. Some unicode space characters are also not collapsed on the web.

Controversy

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 concern 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.

In academic publications, Elsevier uses French spacing but Springer uses a wider space between sentences than between words.

Effects on readability and legibility

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.

Studies

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".