I've been doing a lot of writing lately, and was surprised to see a colleague of mine adding two spaces after a period. I had learned the "two-space" rule in elementary school, but was taught during college and grad school to only use one space after a period. But, after discussing it with my friend, I started to question whether I was right. Should I instead be using two spaces? How much does it matter?
Cue the internet.
Instead of going into all the details myself, I'll point you to a few places where other people have gone into detail, and highlight a few parts. Basically, however, typewriters used the same amount of space for each letter (monospaced), and so two spaces following a period made it easier to read, but we have proportional fonts now that make the two spaces unnecessary, and even obstructive.
From Farhad Manjoo at Slate:
"Who says two spaces is wrong?" they wanted to know.
Typographers, that's who. The people who study and design the typewritten word decided long ago that we should use one space, not two, between sentences.
Because we've all switched to modern fonts, adding two spaces after a period no longer enhances readability, typographers say. It diminishes it.From Jacci Howard Bear at About.com:
The use of proportionally spaced type makes double spaces after a period unnecessary (if they ever were). The extra spacing is often distracting and unattractive. It creates 'holes' in the middle of a block of text — trapped white space on a smaller scale.And, from Mignon Fogart, the Grammar Girl at QuickAndDirtyTips.com:
Although how many spaces you use is ultimately a style choice, using one space is by far the most widely accepted and logical style. The Chicago Manual of Style (1), the AP Stylebook (2), and the Modern Language Association (3) all recommend using one space after a period at the end of a sentence.
So, the take-home message is to use one space following a period. Full stop.