A while back, I declared my allegiance to the serial comma, and I am ready to take another stand.
I believe that double-spacing after a period at the end of a sentence is outdated, clunky, and typographically unsound. (While I’m at it, I also believe that college football’s postseason format is fraudulent, the designated hitter rule is silly, Conan O’Brien was treated unfairly, and Arrested Development was taken off the air way too soon.)
This is not exactly a cutting-edge opinion, but there are still plenty of people out there using the antiquated post-period double space. This is fine if you’re writing e-mails or crafting ransom notes from magazine clippings, but if you’re creating professional-quality printed materials, the single space is the way to go.
The double space after periods was a standard in the days of typewriters, which used monospaced typefaces in which each letter or grammatical mark, whether a capital M or an apostrophe, is given the same amount of space. The typeface Courier, pictured here with ugly, gaping double-space holes after the periods, mimics a typewriter and is an example of a monospaced typeface. (Note the way the characters line up in columns, delineated here with pinstripes, because of the monospacing.) The thinking at the time was that the double space helped provide a visual break between sentences, but when the computer came along and allowed for more subtle variations in spacing, the double space became obsolete.
Since the advent of the computer, most typefaces are proportional, allotting the appropriate amount of space for each typographic character, including spaces after periods. See the typeface Minion, set with elegant, contemporary single spaces, in the example here.
These days, most style guides, including The Chicago Manual of Style and Associated Press, call for the single space. Another proponent of the single space is Robin Williams (the not-funny female graphic designer and author, not the not-funny male actor), who has written several books on technology and graphic design, such as The Mac is Not a Typewriter, The PC is Not a Typewriter, and The Non-Designer’s Design Book.
You’ll notice that nearly all professionally designed printed materials (books, magazines, newspapers, etc.) utilize the single space. The double space after a period looks especially silly if you are using justified type, which already skews word- and letterspacing to force lines of text into a certain amount of space.
The proponents of two spaces after a period seem to harp on the same point: I was taught that way. Many are trying to stop but can’t. Others refuse to hear reason, desperately clinging to their Sholes & Glidden typewriter in one hand, waving the jagged end of a broken moonshine bottle at you with the other.
In the end, there is technically no right or wrong when it comes to spacing after periods, unless you are obligated to follow one of the many style guides out there that call for the single space. But then again, there’s technically no right or wrong when it comes to wearing tapered jeans and paisley shirts, and people do that, too.