Only One Space!
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.
Huh?
For years you’ve been told to hit two spaces
after periods -
and on a typewriter you should. But a computer
is not a typewriter!
On a typewriter, all the characters are mono-spaced; 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 mono-spaced, 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 mono-spaced) 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:
Mono-spaced Font
letters line up in columns
each letter takes up a proportional amount of spaceMono-spaced Font Sample - Courier New
Notice with this font 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 mono-spacing is what makes it necessary to use two spaces to separate sentences.
Proportional Font - Times New Roman
This paragraph uses a font with proportional spacing. Each character takes up a proportional amount of the space available. Therefore the single space between sentences is enough to separate them visually, and two spaces creates a disturbing gap.
The one-space rule applies to all punctuation spacing (after colons, semi-colons, question marks, quotation marks, exclamation points, etc.)
What really convinced me was looking at professionally published materials. If you look at any magazine or book on your shelf, you will never find two spaces between sentences. It doesn't take long to break the habit and soon you will find yourself noticing when people DO put two spaces!
The Mac Is Not a Typewriter by Robin Williams (Berkeley: Peachpit Press, 1990) has been on my shelf since it was published. The Mac Is Not a Typewriter Second Edition was released by Peachpit Press in April 2003. Robin Williams has also written a version for PC users: The PC Is Not a Typewriter.
More resources:
Word Processing Basics- Not a typewriter (first paragraph)
Nuts and Bolts of College Writing - Mechanics - Spaces between sentences
University Publications Typography Guide
Writing for and about Western Michigan University - Typography do's and don't's
My Design Primer: One Space or Two?
One Space or Two? Rules of DTP
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Contact Paula Barnard at Pioneer Elementary School, Arlington Public Schools, Arlington, WA, USA
Updated 06/17/2005