How many spaces should come after a period/full stop?

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?

Solution 1:

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.

Solution 2:

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
http://www.chicagomanualofstyle.org/CMS_FAQ/OneSpaceorTwo/OneSpaceorTwo03.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.)

Solution 3:

Robert Bringhurst has this to say about the subject in The Elements of Typographic Style:

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.

Solution 4:

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.