Dashes can be used to set off material in
the midst of a sentence. However, one should try to avoid using them at
all. When choosing between dashes and other forms of punctuation (such
as commas and parentheses), dashes should be used sparingly and primarily
when the material deserves special emphasis. By contrast, parenthetical
ideas may be lost. In typing or word processing, a dash is formed by placing
one space before and one space after two consecutive hyphens.
Incorrect:
The judge knew the defendant--she had been his third wife--and he therefore
recused himself.
Correct: The judge
knew the defendant -- she had been his third wife -- and he therefore recused
himself.