In the past — or at least, when I was in elementary school — periods/full stops were followed by two spaces. Lately, it's become more and more common to see just one space. In the modern world, should we still use two spaces between sentences, or is just one okay? Does it depend on the situation? Or are both acceptable, with the choice simply coming down to personal preference?
Actually, I feel a few of the other answers here (and even the question) are a bit simplistic: there's more to this issue than is indicated by the latest editions of the Chicago Manual of Style or Bringhurst's The Elements of Typographic Style. In lieu of a very long answer, let me point to the (long) Wikipedia articles on exactly this issue:
- Sentence spacing
- History of sentence spacing
- Sentence spacing in language and style guides
- Sentence spacing in the digital age
My (inadequate) summary would be something like the following:
The traditional typesetters' convention was to use a (single) longer space between sentences than between words. For instance, CMoS 1911 still recommends a 3-em space between words and an em-quad between sentences.
With the introduction of the typewriter (invented in the late 19th century), many typographical niceties were lost: the typewriters produced monospaced (fixed-width) text, and the only choice was between one space and two. Many people felt a single space wasn't sufficient to see the gap between sentences at a glance, so double spacing came into vogue.
Today, with proportional (variable-width) fonts, two spaces is no longer necessary, and can look distractingly too wide. Modern tools allow more choice than between exactly "one space" or two. In particular, TeX and LaTeX have got it right since the 1980s: they typeset a slightly longer space between sentences (though this can be turned off). HTML ignores multiple consecutive spaces anyway. (Sometimes fonts try to be smart and have the period character itself have a wider space following it, but this isn't ideal: there can be periods within a sentence, because of abbreviations etc.)
Even shorter summary (my opinion):
Don't use two spaces unless you're using a fixed-width font like a typewriter. If forced to choose only between one space and two, choose one. But if your typesetting system supports it, have a wider space between sentences.
Both are still acceptable, though the two-space style has been falling out of favor with the advent of variable-width fonts.
From Common Errors:
However, when justified variable-width type is set for printing it has always been standard to use only one space between sentences. Modern computers produce type that is more like print, and most modern styles call for only one space after a period.
The Chicago Manual of Style agrees in these two Q&A segments: http://www.chicagomanualofstyle.org/CMS_FAQ/OneSpaceorTwo/OneSpaceorTwo01.html
The latter states:
The view at CMOS is that there is no reason for two spaces after a period in published work. Some people, however—my colleagues included—prefer it, relegating this preference to their personal correspondence and notes.
So yes, it basically falls to personal preference, but one space is becoming more and more prevalent.
(It's worth noting that all HTML renderers I know of automatically condense multiple spaces into one, so it would actually take some effort to get the double-space style to render on the web.)
2.1.4 Use a single word space between sentences.
In the nineteenth century, which was a dark and inflationary age in typography and type design, many compositors were encouraged to stuff extra space between sentences. Generations of twentieth-century typists were then taught to do the same, by hitting the space character twice after every period. Your typing as well as your typesetting will benefit from unlearning this quaint Victorian habit. As a general rule, no more than a single space is required after a period, a colon or any other mark of punctuation. Larger spaces (e.g., en spaces) are themselves punctuation.
The rule is usually altered, however, when setting classical Latin and Greek, romanized Sanskrit, phonetics or other kinds of texts in which sentences begin with lowercase letters. In the absence of a capital, a full en space (M/2) between sentences will generally be welcome.
Before I first read this many years ago, I had always used two spaces after every period (as I had been instructed by my middle-school typing teacher). Since then, however, I’ve observed that a single space after a period is used in almost all professionally typeset materials (books, magazines, etc.), and I’ve changed my habits.
I continue to use two spaces after a period when writing in a
monospace font, because I feel monospaced text is more readable this way, but I use a single space whenever I’m using a proportional font.
It seems that four or so observations have not yet made it into this thread, so let's add them:
Much printed writing (magazines, newspapers) is done with full-width left and right aligned text. This induces a natural (or not) length space after the period which is different in size in each sentence. Here the use of double spaces after periods should be avoided.
The habit of adding an extra space for visible clarity comes mostly from monospaced fonts. Since about all typewriters used to be monospaced and further in history, type setting used to be monospaced too, the extra space had a benefit. Now many (older?) people still have this habit.
In type setting, kerning has always been very important. Kerning is about how much particular letters or punctuation should be apart. A dot should be closer to its preceding letter, double "ff" should be kerned closer than double "dd" for instance and the space before a capital should be larger than a space before a small letter. This automatically introduces a larger space between full stop and first letter in next sentence. Watch closely: a next sentence starting with a quotation character should get a smaller space.
With the introduction of computer type writing (not type setting!) and proportional fonts, a heated debate was and is going on about kerning and the inability to add kerning to fonts or the reluctance of font designers to do so. However, in proportional fonts and online editing, one should leave kerning (and thus: spacing) to the rendering engine, whether to paper or to screen. Screen however has limited possibilities, but with text, kerning is on its way back due to better support in text writers and has always been around for professional type setters (LaTeX and some Adobe products).
Conclusion: double space after a full stop is a cosmetic habit of the typewriting age and before, and should not be used in online writing or proportional / kerned writing.
I used to be a stickler about this in my own writing and when editing others writing as well, but especially as the computer has taken the place of the typewriter in my writing (showing my age a bit) and as the brevity of Twitter has influenced my other writing (in a good way, mostly) I've come to see the second space as a waste of space.
One nail in the second space's coffin, for me, was watching this video with Microsoft's ex-typography guru, Bill Hill. He says (transcribed):
I single-space after a period. Double-spacing comes from the days when we had typewriters, and the spacing was kind of gross because typewriters are mono-spaced, right? So that came from those days.
I don't know any typographer who does a double-space after a period, the same way no typographer (or nobody who knows anything about type) would ever use underlining as a way of emphasizing, because you break the word shape. Underlining, again, is one of these things that harks back to the days of typewriter (sic), because underlining was the only kind of emphasis you had. But in good typography, in books or magazines or whatever, people use italics or bold for emphasis, not -- never, never, never, never underlining. Underlining is something you do with a pen when you're reading something yourself 'cause it's an emphasis you can do, or something you do with a typewriter because it's the only one you've got, but never in typeset type, it shouldn't be [used].
I used to be an editor, a proof-reader, at a paper in Scotland called "The Scotsman". "The Scotsman" is kind of a weird thing, I used to be a writer there as well; they did this survey once, there was a reading age required to read various newspapers. So they had "The Sun" -- if you're at the reading age of six, I think, you could read "The Sun". The "London Times" I think you needed a reading age of at least eleven. "The Scotsman" you needed a reading age of thirteen; it was kind of the most erudite paper in the country, and they were always incredibly fussy about the typesetting, the way it was done.
So you kind of learn that stuff, and the double-space is kind of ugly, because a space is not a fixed thing, right? Because, you know, once the application has taken the string of characters and then said "OK, I have to break this string here, I really have to hyphenate this word, or route this word down to the next line. OK, now I have to space out, right? And spacing is one of those things that floats like that, so two spaces is compounding the floating-error of one space, so it's not a good thing to use. That's my story and I'm sticking to it.
I always thought that an extra space following the period at the end of a sentence and before the start of a new one, as opposed to a single space after a comma or a semicolon, etc. is there to emphasize a slightly longer pause in the rhythm of a language…
And typesetting environments like TEX has always handled that elegantly; only wider-spread applications, like office productivity suites, etc., do not know how to handle it correctly.
As aluded to by one of the respondents, the reason (most likely) that a single space has become common place is due to the fact that HTML won't allow two sequential spaces without a bit of special plumbing, so the second space got lost in a lot of online writing. However now that we are used to it I think it's probably here to stay.
My preference would be for two as I find it a good visual cue of a sentence end.
Without extra space between sentences, how does one tell the difference between (HTML rendering is going to collapse these):
Watch it, Mr. Smith is coming. (one sentence) Watch it, Mr. Smith is coming. (two sentences) disambiguating: (with &nbsp; to force a space) Watch it, Mr. Smith is coming. (one sentence) Watch it, Mr. Smith is coming. (two sentences) i.e. Watch it, Mister. Smith is coming. (two sentences)
I dropped my old school days/typewriter habit of typing two spaces after a period after I read about fonts in The Mac is not a Typewriter by Robin Williams. That was way back in 1991.
Robin explained what many have said in previous answers: typewriter monospaced fonts needed the second space to compensate for not being able to use proportional fonts. In typesetting with proportional fonts, using one space after a sentence has always been the norm.
It's a wonderful book and she also points out some other stylistic customs to follow in manuscripts for a professional appearance.
As an amazon.com review says:
What is important for the non professional typist to know [is to] use "smart" quotes, don't space twice after a period, italicize instead of underlining, create a long (em) dash by typing [shift + option + -]
I find it very odd that there are apparently so many folks who didn't "get the memo" on this even after all these years. Heheh
It's about appearance, not about HTML coding.
Farhad Manjoo has a great article on "Why you should never, ever use two spaces after a period."
Mr. Manjoo claims that:
Every modern typographer agrees on the one-space rule.
While the two-space rule was adopted during the typewriter era of monospaced fonts, it should go the way of the dodo bird given the adoption of proportional fonts.
Because we've all switched to modern fonts, adding two spaces after a period no longer enhances readability, typographers say. It diminishes it.
Personally, I have converted to the one-space rule even when using a monospaced font. I agree with Mr. Manjoo that:
But I actually think aesthetics are the best argument in favor of one space over two. One space is simpler, cleaner, and more visually pleasing (it also requires less work, which isn't nothing).
For most uses, there's no need for a double space.
A well defined font will handle the spacing between characters with kerning, and adding a double space should be unnecessary. If the font you use has such poor kerning that you can't see the period or sentence structure without two spaces, just use a better font. For normal prose, it's just something you shouldn't need to worry about.
Of course, if you're composing concrete poetry or advertising copy, you may have to worry after all.
Others have discussed the typographical issues; I have nothing to add there.
Two spaces are a pain on computers because they require extra, special logic rules for the computer to process correctly. It's not just HTML: two spaces were a pain for the earliest word processors. When the computer sees two spaces, it doesn't know if it's the end-of-sentence rule, or if the user is trying to make columns line up or do some other special formatting. It requires some extra logic when you get to the end of a line: if a line ends with the end of a sentence, we don't want to leave an extra gap at the end of that line, making it uneven with lines above and below, and we don't want to carry the space down to the next line. Etc. Of course writers of word processing software have long since come up with solutions to these problems, but in the early days it could be an issue.
Yes, I was taught this rule in typing class too, back in the 1970's. I think it was simply an unnecessary, nuisance rule back then, and more so now. It's one of those rules that is mostly followed because it is a rule rather than because there is any good reason for it.