Questions about commas outnumber all other Grammar Cop questions. Why is the comma so confusing? For one thing, usage and preferences vary. One editor may prefer all but the simplest clauses be offset by commas while another may be a comma minimalist. Author Steve Berry once told me he’s the self-proclaimed comma-kasee. He rarely uses a comma and sells a lot more books than I, so who am I to judge?
Here are a few basic rules to help you. Keep in mind, however, no matter what you read or hear, your publisher has the final authority. Only debate a comma placement when it is a matter of changing the sentence’s meaning. Before you debate with an editor, be sure you have a clear understanding of clauses and sentence structure.
Comma Rules in a Nutshell:
An independent clause (Subject + Verb) doesn’t need a comma. A dependent clause does.
Consider this paragraph:
My backpack weighs a ton. The straps, which bear the weight of six textbooks and a laptop, must be reinforced. I wouldn’t wear a backpack but need my hands free for the handlebars of my bicycle. No matter how often I organize and repack the books, I have no space available for my iPod.
The first sentence is easy. It’s a simple, independent clause. The second sentence is a compound sentence because we add the dependent clause modifying the subject straps. The dependent clause, so named because it’s not a complete sentence on its own, should be set aside with a pair of commas (think of them as parentheses). If you delete the dependent clause, the sentence still stands: The straps must be reinforced is an independent clause.
Unless a dependent clause is used as an introductory clause, it should be offset by a pair of commas, one at the beginning and one at the end of the clause. The straps, which bear the weight of six textbooks and a laptop, must be reinforced. Commas aren’t necessary in I wouldn’t wear a backpack but need my hands free for the handlebars of my bicycle. “I” is the subject of both wouldn’t wear a backpack and need my hands free. If written as two independent clauses, it would need a comma before the conjunction but. I wouldn’t wear a backpack, but I need my hands free for the handlebars of my bicycle.
Commas have other uses, too, i.e. separating items in a series: Inside my backpack are pencils, a calculator, textbooks, and a laptop.
A rule of thumb is write the sentence first without commas. If it makes sense without a pause, leave it alone. If you find the sentence convoluted and confusing, you need a set of commas.