Two spaces after a period, or one? Is that the question?
Whether 'tis nobler in the mind to suffer
The slings and arrows of outraged typographers,
Or to delete spaces against our typing traditions,
And by opposing end them? To type: to delete;
No more; and by doing so to say we end
The heart-ache and the thousand natural shocks
That finger is heir to, 'tis a convention
Devoutly to be wish'd. To type, to compose;
To space: perchance to delete: ay, there's the rub;
For in that space or lack what dreams may come
When we have written our immortal prose,
Must give us pause: there's the respect
That makes calamity of so long life;
For who would bear the whips and scorns of time,
The oppressor's wrong, the proud man's contumely,
The pangs of despised love, the law's delay,
The insolence of office and the spurns
That patient merit of the unworthy takes,
When he himself might his spaces make
After a bare full-stop?
Writing in Slate, Farhad Manjoo argues that only a philistine would place two spaces after a period. Then Megan McArdle, in The Atlantic, quoting heavily from Tom Lee's blog Manifest Destiny, comes down hard on the other side.
And the world of Twitter is agog.
Back in the early sixties, when I was learning to set type by hand, I was taught to use an en space after a period. This provided slightly more space between sentences than that between words (generally divided by a 3-em space... one-third of an em space, a square). Spacing changed, of course, during the process of justifying the line, but the rule of thumb was that you could get away with more space after a period than between words. The trick was to keep the spacing in each line visually congruous with all of the other lines.
From a printer's point of view, the Great Space Debate is stupid: space is fluid, simply one of the tools available for creating a pleasing page. The amount of space anywhere is variable--which is why a job case contained even 4- and 5-em spaces, and hair spaces made of brass and copper.
Though, in the heat of the moment, at the height of our passion, we argue about this with strident voice and valorous heart, "Someday we'll look back on this and it will all seem funny." Or so Bruce Springsteen says.