As demonstrated, too few or too many commas can cause mayhem, but you must also be careful that you don’t commit a punctuation faux pas, the comma splice. When your parents and grandparents attended college, they might have been warned that a comma splice in an English essay would result in an automatic “F” on the paper. Yikes!

While you may not fear grammar mistakes to this degree, you should still be careful when it comes to writing compound sentences that need both a comma and a conjunction. If you write a compound sentence without the conjunction but add the comma, you have made the dreaded error—the comma splice.

You might be asking “What’s the big deal? Why was it such a weighty mistake?” The answer is partly that misplaced punctuation such as a comma can obscure or change the meaning of sentences. Also that particular rule about not joining two independent clauses with a comma is a simple rule to remember. You learned this rule early in school, and it’s an easy rule to apply.

The good news is that you can avoid all the worry by practicing good proofreading skills. One way to look for comma splices is to use a colored marker and mark every compound sentence in your paper. When you finish, look at each one closely to make sure you have added not only the comma but also the conjunction that joins the two sentences.

Suppose you write a sentence like this one:

The football player was helped off the field, the ambulance picked him up on the sidelines.

This example contains a comma splice. It’s easily corrected, however, by adding a conjunction as follows:

The football player was helped off the field, and the ambulance picked him up on the sidelines.

If a sentence contains two independent clauses linked by a conjunction (and, as, but, for, nor, so, or yet), usually a comma belongs before the conjunction. (See Use a Variety of Correctly Structured Sentences—Compound, Complex, Compound-Complex in the Related Resources for more information on sentence structure.)