One space or two? It may never have occurred to you that there should even be a question like this. After all, wasn't everyone always taught that you need two spaces after a sentence when you are typing?

Well, many of us were taught that. And for good reason--we were learning to type on a typewriter. Because typewriters produce monospaced type, putting an extra space after a period or question mark made sense. Monospaced type is text produced by characters that are evenly spaced. A "W" takes up just as much room as an "l". Thus, around skinny letters there was more space than around wide letters. To clear everything up, it was decided that an extra space should be added after a sentence to make it easier to see where one sentence ended and the next began.

However, even in the age of the typewriter, professionally typeset text only used a single space after a sentence. And today, we have proportionally spaced fonts. Now, characters are spaced according to their width, and this is done automatically by our computers. Since the text does not incorporate extra space around the letters, the confusion over where the sentences end is eliminated. Thus, we really only need one space after a period or question mark.

This can be a difficult habit to break, but there are significant benefits to only using one space. When two spaces are used, you can create gaps in the block of text, which can make your text less readable. Your reader may be unconsciously distracted by these holes. Even worse, you can create "rivers" of white space in your document. This also makes your text less attractive and professional looking.

Look at these examples. Decide for yourself if you find the double spacing after the sentences distracting.

One Space
Next time you fuel up, don’t top off your gas tank. You may feel that you are getting every last drop you can into your tank. But you actually are not putting much more gas into your car. You also are risking problems ranging from fuel smells in your car’s interior, to eliminating the available space for fuel expansion as it heats. It is also harmful to the environment, as it causes more vapors to be released into the atmosphere.

Two Spaces
Next time you fuel up, don’t top off your gas tank.  You may feel that you are getting every last drop you can into your tank.  But you actually are not putting much more gas into your car.  You also are risking problems ranging from fuel smells in your car’s interior, to eliminating the available space for fuel expansion as it heats.  It is also harmful to the environment, as it causes more vapors to be released into the atmosphere.

The difference is subtle, but important. The first example does not have the distracting gaps that the second example does. If you examine the text that you read every day--in magazines, books, and other publications--you will find that the overwhelming majority only use one space after a sentence.

Of course, no desktop publishing rule would be the same without having exceptions. You may want to consider using two spaces after your sentences if you are using a monospaced font, you are typing a book manuscript, business proposal, or term paper, or are using a typewriter. Also, follow your gut instinct. If something just doesn't look right one way, feel free to do whatever it takes to make it look good and to increase its readability.