APOSTROPHE Apostrophes are used to mark the omissions of letters and figures in the contractions of words and word combinations. Can't couldn't they've wasn't wouldn't I'd don't didn't we'd ass'n he'd it's class of '04 However, apostrophes are not used in abbreviations or the shortened form of some words. Sgt. (rather than Sg't) phone Frisco Coon copter Halloween Apostrophes are sometimes used to form the plural form of letters, numbers, words, and abbreviations. x's and o's 2 by 4's three 7's or 11's two CD's or DVD"s do's and don'ts Apostrophes are used to create the possessive form of nouns and indefinite pronouns, abbreviations, phrases, quotations, and words constructed from numerals. Click here for details on possessives.