A. Use the hyphen with the compound numbers twenty-one through ninety-nine, and with fractions used as adjectives.
CORRECT: Sixty-five students constituted a majority.
CORRECT: A two-thirds vote was necessary to carry the measure.
B. Use the hyphen with the prefixes ex, all, and self and with the suffix elect.
CORRECT: The constitution protects against self-incrimination.
CORRECT: The president-elect was invited to chair the meeting.
C. Use the hyphen with a compound adjective when it comes before the word it modifies, but not when it comes after the word it modifies.
CORRECT: The no-holds-barred argument continued into the night. The argument continued with no holds barred.
D. Use the hyphen with any prefix used before a proper noun or adjective.
CORRECT: His pro-African sentiments were heartily applauded.
CORRECT: They believed that his activities were un-American.
E. Use the dash to indicate an abrupt change of thought. In general, however, formal writing is best when you think out what you want to say in advance and avoid abrupt changes of thought.
CORRECT: The inheritance must cover the entire cost of the proposal—Gail has no other money to invest.