Erik Barzeski asks why people still put two spaces after a sentence. Eric goaded Nick into insisting they shouldn’t. I think it shouldn’t have to matter. Fact: There should be more space following sentence-ending punctuation (period, exclamation point, colon, semicolon, question mark, what have you) than between words. Fact: Computers are smart enough to figure this out for you. In fact, this is the sort of thing they’re much better than humans at.
Commenters on Erik’s entry point out that style manuals still tell you to use two spaces, even though one is “all that’s required.” It’s worth mentioning that style manuals, for the most part, ignore desktop publishing. They’re still assuming that you’re either writing with a typewriter (where two spaces make things more readable) or that you will be professionally published (where the typesetter will add the correct amount of space for you.) Desktop publishing gives the ordinary computer user the ability to royally screw up their own documents. Unfortunately, they usually take full advantage of this.
Nick claims that type designers add extra space after periods to make a single “space” the right thing to use, but given what I know about how computer fonts work, I’m dubious that this works correctly. Somebody needs to explain to me how font software, which works in very limited context, can tell the difference between “I live in St. Louis,” (which needs a thin inter-word space after the first period and “John lives on Rose St. Louis doesn’t.” (which needs a thick sentence-separating space after the first period). Fonts come with glyphs and a complicated set of layout rules for assembling them based on character sequences. But really, it’s up to the text software as a whole–that would be your word processor or Web browser or email program or the OS routines that they make use of–to use the rules of English to figure out where your sentences are, and insert the appropriate amount of space, regardless of how many times you hit the space bar. Computers are good at tasks like this.
HTML is based on SGML, which was designed by Real Publishers back in the 1970’s. So it does the right thing (ignoring the amount of whitespace you used and inserting its own). TeX, which Donald Knuth wrote to help him typeset his books (also in the 1970’s), does the right thing too. Ironically, word processors like Microsoft Word were designed in the 1980’s for desktop computers too small and slow to do anything as complicated as insert whitespace–and you were going to be printing either on a daisywheel or a crappy-looking dot matrix printer, so why did it matter?–so they almost always do the wrong thing when it comes to how Real Documents should look.
(Actually, it’s possible recent word processors get this right too; I don’t know, I haven’t used one in years. I strongly suspect, though that in the name of “backwards compability” and “consistent interface,” they continue to make ordinary people care about stupid stuff like how much space there needs to be after a period to make things readable.)
What do I do personally? I always hit the space bar twice. I used to use one space. Laura said I should use two. She pointed out that two spaces make my text more readable in forums–like email and Usenet–that tend to display exactly what I typed, using a fixed-width type, just like a typewriter or a 1960’s-era teletype (which is what they’re pretending to be). It turns out she was right (and the style manuals agree with her). So now I always use two spaces, and the right thing always happens: When I send email or write news, the extra space helps readability for those who read it in a fixed-width font, and when I’m composing an HTML or LaTeX document, the amount of whitespace I use is ignored and the computer does the right thing automatically.