I have a client whose style guide demands that all documents contain double spaces after periods and colons. When I first noticed this, I asked when the style guide had been updated and whether anyone really follows that standard. Although the style guide is updated every few years, new versions assiduously retain the double space edict. I’ve ask people whether they know the history of double spaces, and almost no one does.

Here’s the story as I understand it. Inserting double spaces after a period and colon are holdovers from the days when people used typewriters, and most typewriters used the Courier font, which devoted the same amount of space to small characters, such as periods and colons, as it did to wide characters, such as W and M. In days gone by, typists were instructed to insert two spaces after a period and colon because it gave readers a subtle, visual cue that they had reached the end of a sentence or phrase.

Today’s modern printers use proportional fonts, allotting different amounts of space to characters depending on their width. Thus it’s simply no longer necessary to insert double spaces after periods or colons because it adds more space to a page than is necessary (unless one still occasionally has need to use Courier or one of the older fonts).

Most people look at me blankly when I explain this. They get it, but they can’t or won’t change their typing habits.

Another problem with using double spaces is that one often ends up having three or four spaces between sentences. This may happen when someone cuts a sentence or two from one document and pastes it into another, taking along with it the double spaces before and after the original cut. I’ve seen documents with a strong of five or six spaces, which makes a page especially difficult to read. And it looks messy. It’s easy to clean up by repeatedly searching for two spaces and replacing them with one.

Quite simply, there’s no need to put two spaces after a period. If you were taught to insert two spaces after a period, try and train yourself to stop doing it. In the long run, your documents will look better.