A contraction is the combination of two words by means of an apostrophe—which usually replaces a letter or two. Common contractions include it’s (it + is), you’re (you + are), don’t (do + not), won’t (will + not), he’s (he + is), and so on.

   Contractions cause people undue grief; many strong writers occasionally mix up their and they’re, your and you’re, and its and it’s. For help on these matters, see the individual words.