Comma splices occur when two complete sentences are joined together with only a comma; comma splices can result in confusion for readers.

Let's consider the following incorrect sentence: The course was difficult, it required five different texts, four 10 page-papers were due during the semester.

You most likely recognized three different thoughts in the sentence:  The course was difficult.  It required five different texts. Four 10-page papers were due during the semester.

Notice that each of those thoughts is a complete clause or sentence with a subject and predicate.  The comma on its own is too weak to hold these sentences together.  This second series of sentences (The course was difficult.  It required five different texts. Four 10-page papers were due during the semester.) is punctuated correctly with periods marking the ends of the sentences. 

So, one way to fix a comma splice is simply to create separate sentences and punctuate them properly.  Let's consider another example:

Incorrect Ex. Bob was abducted by Martians, he was really scared.

Correct Ex. Bob was abducted by Martians. He was really scared.

Using periods shows each idea as separate. Although creating separate sentences is functional, there are many more options that are equally correct, but also allow a reader to show the relationship between or among ideas more clearly or gracefully. 

You can also fix the sentence by adding a conjunction:

Ex. Bob was abducted by Martians, and he was really scared.

In this method, we used a comma and added coordinate conjunction (and), which indicates the ideas are equal in importance. Other coordinating conjunctions include but, for, nor, or, so, and yet, and each adds a difference meaning to the sentence.

The sentence can also be fixed by adding a colon (and re-arranging the sentence in this particular example):

Ex. Bob was really scared: he was abducted by Martians.

This method requires the clause after the colon to modify the clause before it. Why was Bob really scared? He was abducted by Martians. However, using a colon implies a relationship between the two clauses that the other types of correction methods don’t imply. Using a colon implies that the following clause somehow explains, elaborates, or expounds on the information that came directly before the colon.

Another method to fix this sentence is to add a semicolon (as long as the clauses are closely related, which, in this case, they are).

Ex. Bob was abducted by Martians; he was really scared.

This method links the clauses and shows them as closely related, yet separate.

One final way to fix this sentence is to add a subordinating conjunction to it:

Ex. Because Bob was abducted by Martians, he was really scared.

This method changes the emphasis of the sentence. Using a subordinate clause to open the sentence indicates the first part of the sentence is less important information than the last part of the sentence.
 

Determine whether each of the following sentences contains a comma splice or if it is correct.

1. While it was just a mistake, Amy’s pen throw caused her to feel bad.

2. He went to the park, she went to the mall.

3. Sally rode her bike, Bobby was upset because his was broken.

Answers:

1. Correct. This sentence begins with a subordinate clause.

2. Incorrect. This comma splice could be fixed in a number of ways, such as adding a conjunction: He went to the park, but she went to the mall.

3. Incorrect. This comma splice could be fixed in a number of ways, such as adding a period: Sally rode her bike. Bobby was upset because his was broken.
 

Writers may be interested in reading our guide on Comma Splices and Fused Sentences and additional exercises to test your knowledge about comma splices are available here. The media presentation on Sentence Errors by Candice Chovanec Melzow also contains information on comma splices.

Recommended Grammar Website of the Week

This week we also recommend Tina Blue's article What Is a Comma Splice, and How Do I Fix It?  After an introduction that mentions that not all comma splices are incorrect, Blue discusses two ways to deal with independent clauses that appear next to each other to avoid comma splices.  She explores the stylistic effect of comma splices in When Is a Comma Splice NOT an Error?