When I was little, my mother told me that when typing I should put two spaces after a full stop. We were using typewriters and because that’s how what she had learned, I followed suit. For years, right through school and university, I dutifully put two spaces after full stops, even when using a computer.
It wasn’t until I started working that my manager said to only put one space after a full stop. Being a new employee, I changed to the house style. I later found out that the one space/two space argument is one of those hangovers from the days when typewriters ruled the business world. Doing a quick search on the subject reveals that it’s something that a lot of people still struggle with.
Personally, now I’d always use one space after a full stop. The reason? Thanks to modern layout programs and the widespread use of computers, allowing one space after a full stop is enough to rest the eye and make a bit of a break. If you put two spaces in, it looks a bit like a chasm has opened up on the page.
White space is good but in some places it just looks strange (to me, anyway). But as a rule of thumb I’d always go with what your house style guide says. That’s your bible and if it says to put two spaces after a full stop, by Jove, put two spaces.
But I would suggest using one. It’s quicker, for one thing.
According to an article on Slate.com, the two space rule came about because of typewriters. Prior to that (after a few centuries of standardisation), typesetters had decided on the one-space rule. When typewriters came along, one space between sentences was just too small so two were added. Then as typewriters became more popular and widely used, the rule went with it. And now we have the remains of people emphatically stating that two spaces are required after a full stop.
Personally, I’d never go back to using two spaces if I can avoid it. The vast nothingness between the full stop and the following capital letter unnerves me, but to each their own. Above all, consistency is key.