1. Only use commas when required by the following rules.

        serialComma
      1. In a series of three or more terms with a single conjunction, use a comma after each term except the last.

        1. Use “and” only once, right before the last term.

          red, white, and blue
          honest
          , energetic, but headstrong
          He flicked it open
          , held it up in the air, and clicked it.
      2. Use commas to set off names in direct address.

        Direct address means when the speaker is speaking directly to someone.

        What about you, Neville?
        Right then
        , Mr. Potter, try this one.
        Miss Granger, five points will be taken from Griffyndor.
      3. Use commas to set off brief exclamations or introductory phrases.

        Honestly, don’t you two read?
        Well, a second’s there to take over if you die.
        Strangely, that’s the second time in a week.
        In addition to detention, fifty points will be taken from Griffyndor.
      4. Enclose parenthetic expressions (sometimes called nonrestrictive clauses) between commas.

        A parenthetic expression is one that you could take out of the sentence, and what’s left would still be a sentence. It adds nonessential information.

        Harry
        , instead of feeling pleased and proud, felt quite sure there had been a horrible mistake.
        Harry, who was starting to feel warm and sleepy, looked up at the High Table again.
        The Great Hall, where the Halloween decorations were hung, put Hermione out of their minds.
        Ron and Hermion
        e, when they had found a place in the stands, couldn’t understand why they looked so grim and worried.
        Zaphod Beeblebrox, President of the Imperial Galactic Government, sped across the seas of Damogran, his ion drive delta boat winking and flashing in the Damogran sun.
        1. If a parenthetic expression is preceded by a conjunction, place the first comma after the conjunction, not before it.

          He saw us coming and, unaware that we had learned of his treachery, greeted us with a smile.
        2. Some parenthetic expressions are called appositives. Enclose appositives between commas.

          An appositive is a parenthetic expression that names, renames, or modifies the noun that precedes it.

          Zaphod Beeblebrox, adventurer, ex-hippy, good timer, was often thought to be completely out to lunch.
        3. Place a comma before a clause that begins with an -ing verb

          (called the progressive or continuous tense) -- this is called a nonrestrictive participal phrase.

          Zaphod Beeblebrox paced nervously up and down the cabin, brushing his hands over pieces of gleaming equipment and giggling with excitement.
      5. The abbreviations etc. and jr. are always preceded by a comma and, except at the end of a sentence, followed by one.

        For some reason, if a strag (strag: non-hitchhiker) discovers that a hitchhiker has his towel with him, he will automatically assume that he is also in possession of a toothbrush, face flannel, soap, tin of biscuits, flask, compass, map, ball of string, gnat spray, wet weather gear, space suit, etc.
      6. Place a comma before a conjunction which combines two parts of a sentence which could each be a separate sentence (these are called independent clauses).

        He’s got lots o’ rats an’ some brandy for the journey, anI’ve packed his teddy bear in case he gets lonely.

        Fred and George have lost loads of point
        s, but people still like them.
        1. Sentences of this type are often better if rewritten:

          Although Fred and George have lost loads of points, people still like them.
      7. Put a comma before and after a year when it is part of a date.

        December 7, 1941, is a date that will live in infamy.
      8. Use a comma after the street before the city, after the city before the state (and also after the state if the sentence continues).

        In Hillsborough, California, there is a little school with a big reputation.
        I live at 445 Cypress
        Ave., Half Moon Bay, California.
      9. Use commas in a large number to break it into groups of three digits.

        The Hitchhiker's Guide to the Galaxy says that if you hold a lungful of air you can survive in the total vacuum of space for about thirty seconds. However it goes on to say that what with space being the mind boggling size it is the chances of getting picked up by another ship within those thirty seconds are two to the power of 267,709 to one against.
      10. Place a comma after the greeting and after the closing in a letter.

        Dear Mr. Potter,

        We are pleased to inform you that you have been accepted at Hogwarts School of Witchcraft and Wizardry.

        Sincerely,
        Albus Dumbledore
      11. Use a comma when you have two or more adjectives describing the same noun.

        Filch owned a cat called Mrs. Norris, a scrawny, dust-colored creature with bulging, lamplike eyes just like Filch’s.

redundantComma