The Big Bad Three of Punctuation
Easy rules will help you determine whether you need a comma, semicolon or colon.
Use the comma to separate independent clauses joined by a conjunction. The coordinating conjunctions are but, and, so, for, nor, yet and or. Place the comma before the conjunction.
I needed to talk to the boss, but she was in a meeting.
Use the comma to set off the nonrestrictive element in a sentence.
I gave the approval letter to Jean, the woman with the long hair, on the third floor.
Use the comma to set off conjunctive adverbs and adverbial phrases.
I went to the door to see him; he turned, however, and walked away.
The Toledo office, on the other hand, is doing great.
Use the semicolon to separate related independent clauses that are not joined by a coordinating conjunction.
I invited the Douglas family; I left the Johnsons off the list.
Francis brought bagels with raisins, walnuts and cranberries; six pints of coffee; four bags of cinnamon twists, complete with frosting; and a dozen doughnuts.
Use the colon to introduce information or to elaborate on an element in a sentence. Colons usually fall before a listing, before direct quotations in formal essays or after the salutation in formal correspondence.
There are several things we still need: Four reams of paper, six packs of strapping tape, three box cutters, eight balls of twine and two red markers.