Microsoft has decided that it will officially join the ranks of those who consider it an error to put a double space after the end of a sentence.
(Although when I recently typed a sample paragraph in Word with the offending two spaces, no red squiggly line appeared; maybe the change has yet to be implemented, or I need to update my version of Word.)
Double versus single spacing is one of those long-running controversies that get people — not just word nerds — all hot and bothered. There are those who get positively irrational about it, as often happens with things that don’t actually matter (like whether or not to use an Oxford comma, in most circumstances).
The explanation usually given for moving away from double spacing is the fixed (or monospace) nature of typewriter fonts, which no longer applies in the more flexible digital world, although this article from the people at the Chicago Manual of Style suggests that it is a bit more complicated than that.
Whatever the history, the first thing most professional editors will do with the piece you have submitted is to use ‘find and replace’ to reduce end-of-sentence spacing from double to single.
If you insist on keeping two spaces, Microsoft may still allow you to bypass the new default rule (if you can find where to do that in your settings — I can’t seem to), or you could use the hacks in this post.
Better yet, go with the cool kids and use just one space between sentences.
Thanks to John Hightower of Lanier Ford Shaver & Payne PC and Jennifer Prouse of Minden Gross LLP for the resources!