Writers use the comma as follows:

• With a coordinating conjunction (and, or, but, for, nor, so, yet) to join independent clauses (unless the clauses are very short).

  The judge entered the courtroom more than an hour late, and the members of the press expressed annoyance at the delay.

  The subway had been operating for months, but Elsie had not yet learned how to use it.

• To set off items in a series of three or more.

  The big, red, hairy setter jumped through the glass pane.

  The weeds grew in the garden, on the lawn, and even in the woods.

• Used in pairs, like parentheses, to set off nonessential material embedded within a sentence.
   
  • Non-restrictive Clauses or Phrases: (non-essential information) = use commas

    Jodi usually parked her car, with its fancy wheels and custom grill, near the library.

    The dog, an energetic Australian shepherd, jumped the fence with ease.
     

  • Restrictive Clauses or Phrases: (essential information that restricts or limits or identifies the meaning of a word nearby) = no commas

    Colleges with more than 45,000 students are rare.

    The student with hepatitis has been barred from the dining facilities.

• Used to set off material at the beginning or at the end of a sentence. This "rule" is subject to editorial preference. In general, however, if the introductory words contain more than one preposition or if the lack of a pause following introductory words leads to confusion, or if the sentence begins with a dependent clause, use a comma.

  Defeated, the team shuffled sadly into the dressing room.

  In the middle of a dark and stormy night, Jack heard a scream.

  The riverbed was a patchwork of mud cakes, parched by the long summer drought.

  

Commas and FANBOYS
You do not need a comma between every coordinating conjunction. Use the comma / coordinating conjunction combination only to:

• separate items in a series of three or more
  or

• to separate independent clauses.

Do not use this combination to separate pairs of words or phrases!

Dreaded Comma Splices (and how to fix them)
A comma splice occurs when two independent clauses are joined by a comma:

Pat lived in terror of comma splices,
she didn't know how to fix them.

• Solution 1: use a comma and a coordinating conjunction:

  Pat lived in terror of comma splices, but he didn't know how to fix them.

• Solution 2: use a colon or semicolon, depending upon the relationship:

  Pat lived in terror of comma splices; she didn't know how to fix them.

• Solution 3: use a semicolon, a conjunctive adverb, and a comma:

  Pat lived in terror of comma splices; however, he didn't know how to fix them.

• Solution 4: use a period:

  Pat lived in terror of comma splices. She didn't know how to fix them.

• Solution 5: subordinate one of the clauses:

  Pat lived in terror of comma splices because he didn't know how to fix them.

  Even though Pat lived in terror of comma splices, she didn't know how to fix them.

  Pat, a guy who lived in terror of comma splices, didn't know how to fix them.

• Clause: a group of closely related words containing a subject and a finite verb.
  • Independent Clause: a clause that makes sense as a sentence in itself.
    • Susan loves her English class.
  • Dependent Clause: an independent clause plus a subordinating conjunction.
    • although she is nervous about her first paper
• Subordinating Conjunctions: after as, although, as if, as long as, because, before, even if, even though, if, if only, in order that, now that, once, provided, rather than, since, so that, than, that, though, 'till, unless, until, when, whenever, where, whereas, whether, while
• Coordinating Conjunctions: for, and, nor, but, or, yet, so (remember "fanboys")
• Conjunctive Adverbs: consequently, furthermore, however, moreover, nevertheless, otherwise, then, therefore, thus, furthermore, similarly, etc.

Updated: 08.18.07