There was a point in time when I used to put two spaces after the period in a sentence. It was a habit I had learned because of teachers who stressed the need for a double-space to increase reading clarity. Then, in high school, one of my English teachers explained to me that this was wrong and outdated. There wasn’t really an argument in her mind about it — placing two spaces after a period was just no longer necessary because everybody in class had a computer (and nobody wrote essays or reports using Courier).

As Slate explains in a recent article about the outdated writing style:

The problem with typewriters was that they used monospaced type—that is, every character occupied an equal amount of horizontal space. This bucked a long tradition of proportional typesetting, in which skinny characters (like I or 1) were given less space than fat ones (like W or M). Monospaced type gives you text that looks “loose” and uneven; there’s a lot of white space between characters and words, so it’s more difficult to spot the spaces between sentences immediately. Hence the adoption of the two-space rule—on a typewriter, an extra space after a sentence makes text easier to read. Here’s the thing, though: Monospaced fonts went out in the 1970s. First electric typewriters and then computers began to offer people ways to create text using proportional fonts. Today nearly every font on your PC is proportional. (Courier is the one major exception.) Because we’ve all switched to modern fonts, adding two spaces after a period no longer enhances readability, typographers say. It diminishes it.

Of course, not everyone agrees on the single-space vs double-space argument as you will quickly see in the Slate article’s comments. As for me, I’ve given up the double-space practice for a while now and find it incredibly distracting in my reading when I see that somebody has included an extra space between sentences.