One space between sentences
Adapted from Robin Williams, The Mac Is Not a Typewriter (Berkeley: Peachpit Press, 1990)

Use only one space after periods, colons, exclamation points, question marks, quotation marks—any punctuation that separates two sentences.

What? you say! Yes—for years you’ve been told to hit two spaces after periods, and on a typewriter you should. But this is no typewriter.

 

On a typewriter, all the characters are monospaced; that is, they each take up the same amount of space – the letter i takes up as much space as the letter m. Because they are monospaced, you need to type two spaces after periods to separate one sentence from the next. But …

 

On a computer (unless you’re using the fonts Monaco or Courier, which are monospaced just like a typewriter and what would you want to use those for anyway) the characters are proportional; that is, they take up a proportional amount of space—the letter i takes up about one-fifth the space of the letter m. So you no longer need extra spaces to separate the sentences. Take a careful look at these two examples:


Notice in this paragraph how the letters line up in columns, one under the other, just as on your typewriter. This is because each character takes up about the same amount of space. This monospacing is what makes it necessary to use two spaces to separate sentences.
(Font = Courier New)


This paragraph, however, uses a font with proportional spacing. Each character takes up a proportional amount of the space available. Thus the single space between sentences is enough to separate them visually, and two spaces creates a disturbing gap.
(Font = Times New Roman)

 

Of course, this one-space rule applies just as well to the spacing after colons, semi-colons, question marks, quotation marks, exclamation points, or any other punctuation you can think of. Yes, this is a difficult habit to break, but it must be done.

 

Take a look at any magazine or book on your shelf—you will never find two spaces between sentences (the only exception will be publications or advertisements produced on a computer by someone who was still following typewriter rules).

 

Click here for a more detailed case made against using two spaces after a period.