As I’ve said before, grammar and mechanics are just as much a part of craft as plot, compelling characters, and well built worlds. The comma is one hell of an important punctuation mark. Commas indicate pause; if you give pause where there is none, your readers are likely to trip over your words, sending them stumbling along through the sentences that follow. Keep these three major rules in mind while you’re writing.
An independent clause is a set of words that include a subject and a verb. It must express a complete thought. To connect two independent clauses within the same sentence, insert a comma after the first clause, followed by a coordinating conjunction (i.e. and, or, but). Here’s an example:
Lewis loved to ride his bike, and Elizabeth loved to watch him.
If I had simply written:
Lewis loved to ride his bike, Elizabeth loved to watch him.
–I would have been committing the fateful crime of comma splice. A comma splice occurs when two independent clauses are connected by a comma with no coordinating conjunction.
Use a comma to separate phrases or words in a series
You’ve seen this a billion times before. A collection of items, locations, or names should include commas between each word or set of words in the series. See what I did in that last sentence? Now, let me tell you right now that if someone says to omit the last comma (between the second and third words, for instance), you tell them to stuff it and run far, far away. Okay, that’s a little rude, but you get my meaning. The last comma in the series is known as the serial comma or the Oxford comma, and it is 100% necessary unless you are a master of the English language or plan to carefully review every sentence in your manuscript for errors. There are so many ways to befuddle your readers by excluding the serial comma. See below.
Use a comma to set off an introductory phrase or an interjection
While some short introductory elements may not need a comma, many longer ones do.
Rushing towards the crash, Tara called in anguish for Kevin to answer her.
The comma in the sentence above sets off the introductory phrase “Rushing towards the crash” and gives an appropriate pause. An interjection, on the other hand, resides inside the sentence instead of at the beginning. Again, see what I did in the last sentence? When placing an interjection, the following rule applies: If you insert one comma before or after, insert another one on the opposite side of the phrase. Otherwise, don’t use any commas at all.
For specific tips on formatting dialogue (which has its own rules for commas), visit my post!