Writers' Guide > Comma Splices


Running sentences into one another with no stop at all is called a fused or run-on sentence.  Few people make this mistake.  However, one variation of the run-on sentence is a very common error in student writing.  This is the comma splice - incorrectly joining two complete sentences with only a comma.


Students who make this mistake often have great difficulty overcoming it.  This is quite understandable because we often think of two closely related ideas (with one immediately following the other) as a single, continuous thought; therefore, we are tempted to "splice" them together with only a comma.  Nevertheless, the two sentences that express the ideas are grammatical units and either must be separated or must be joined in an appropriate way.  A comma is not enough between two complete sentences unless a coordinat­ing conjunction (and, but, or, nor, for, so, yet) is also used.  In fact, the only time one may correctly use only a comma to connect two independent clauses is in the compound sentence, i.e., one in which the two clauses are connected by a coordinating conjunction.  And the error is considered particularly serious because it suggests that the writer does not know where one sentence ends and another begins, causing no end of confusion for the unfortunate reader.


To prevent comma splices:  Learn to recognize what constitutes a complete sentence (or an independent clause).  When you reach the end of a complete sentence, you have several options.  You can stop, using a period.  You can stop, using a semicolon (the technique that is often used when the two sentences are very closely related or when the second sentence is introduced by a transitional word).  Or you can pause (signified by a comma), insert the appropriate coordinating conjunction, and then go on.


Learn to recognize the types of constructions that cause comma splices.  For example, many students incorrectly splice together sentences when a transitional word or phrase introduces the second sentence.  The examples following and on the back of this page illustrate common causes of comma splices and how to correct them.


comma splice:  This has been a very dry summer, therefore, the supply of water in the reservoirs is low.


explanation:  The comma after summer (before the transitional word therefore) is too weak.  (We don't know whether therefore belongs to the clause before it or the one after it.)


ways to correct:  Use a semicolon to correct the comma splice:  This has been a very dry summer; therefore, the supply of water in the reservoirs is low.  (The comma after therefore stays there.)  Rephrase, using a coordinating conjunction:  This has been as very dry summer, so the supply of water in the reservoirs is low.  Make it two sentences:  This has been a very dry summer.  Therefore, the supply of water in the reservoirs is low.  Make the first sentence a subordinate clause:  Because this has been a very dry summer, the supply of water in the reservoirs is low.

comma splice:  Heavy rain fell throughout the night, by morning every major road was flooded.


explanation:  Although the second statement is a continuation of the idea, the two statements are grammatically independent sentences.


ways to correct:  Make two sentences:  Heavy rain fell throughout the night.  By morning every major road was flooded.  Use a coordinating conjunction:  Heavy rain fell throughout the night, and by morning every major road was flooded.  Make a subordinate clause out of the first sentence:  Because heavy rain fell throughout the night, every major road was flooded in the morning.


comma splice:  Mary kissed Frank, then, for no apparent reason, she slapped him.


explanation:  Again, although the sentences describe a continuous action, they are nonetheless two distinct sentences.  The break should be between Frank and then.


ways to correct:  Use a semicolon:  Mary kissed Frank; then, for no apparent reason, she slapped him.  Use two sentences:  Mary kissed Frank.  Then, for no apparent reason, she slapped him.  Use a coordinating conjunction:  Mary kissed Frank, and then, for no apparent reason, she slapped him.  (The words for no apparent reason constitute a parenthetical phrase or "interrupter," which is set off by commas regardless of the punctuation or structure of the rest of the sentence.)


comma splice:  John studied hard for the test, he failed it anyway.


explanation:  Two related (contrasting) sentences are incorrectly connected with only a comma.


ways to correct:  Insert a coordinating conjunction:  John studied hard for the test, but he failed it anyway.  Subordinate one of the clauses:  Although John studied hard for the test, he failed it anyway.  Use a semicolon:  John studied hard for the test; he failed it anyway.


comma splice:  Charlie is not only handsome, he is also rich.


explanation:  Despite the use of "not only . . . also," this construction consists of two grammatically independent clauses.


ways to correct:  Add a coordinating conjunction (i.e., balance not only with but also):  Charlie is not only handsome, but he is also rich.  Compress the idea:  Charlie is not only handsome but rich.  Use a semicolon:  Charlie is not only handsome; he is also rich.

Rich Turner