English 101 Help > Sentence Punctuation: Avoiding Comma Splices


The comma splice, which is perhaps one of the most common punctuation errors in student writing, consists of running two sentences together with only a comma.  It is a type of run-on sentence, failing to show where one complete thought ends and another begins.

We have already seen (in Sentence Punctuation: Basics) that we may connect two complete thoughts with a comma and a coordinating conjunction (but, and, for, yet, so, or, nor).  We have even seen how – on rare occasions and only if we know what we are doing – we may use only a comma between two short and very closely related sentences.  However, in every other instance, connecting complete sentences (independent clauses) with a comma is incorrect.

Here are examples of comma splices, with suggested corrections.

1.  Mary kissed Henry, then, for no apparent reason, she slapped him.
This is not utterly confusing, but it is technically incorrect and appears overloaded with commas.  We do need commas around for no other reason because it is an interrupting phrase in the clause then . . . she slapped him.  However, since then is not a coordinating conjunction but a transitional adverb, we should insert a semicolon:  Mary kissed Henry; then, for no apparent reason, she slapped him.  The stronger stop provided by the semicolon clearly shows that then belongs with the second clause, not the first.  (Yes, we could also use a period, capitalize then, and create two sentences.)

2. Darwin's theory hypothesizes that humans evolved from lower life forms, however, its validity has been frequently challenged.
Illustrating one of the most common types of comma splice, this sentence incorrectly places a comma before a transitional word (however) that introduces the second independent clause.  The punctuation thus fails to show whether however belongs with the second clause or the first clause.  Some possible corrections
> The most obvious  change the first comma to a semicolon:  Darwin's theory hypothesizes that humans evolved from lower life forms; however, its validity has been frequently challenged.
> Use a coordinating conjunction instead of a transitional word:  Darwin's theory hypothesizes that humans evolved from lower life forms, but its validity has been frequently challenged.  The coordinating conjunction but is preceded by a comma; there is no comma after it.
> Rewrite the sentence as a complex sentence with a dependent clause followed by and independent clause:  Although Darwin's theory of evolution hypothesizes that humans evolved from lower life forms, its validity has been frequently challenged.

3.  His actions were not only irresponsible, they were also probably illegal.
This is another very common type of comma splice.  Because "not only . . . also" appears to be one continuous thought, the author uses only a comma between the two independent clauses.  However, the sentence consists grammatically of two distinct independent clauses spliced with only a comma.  Some possible corrections
> Insert a coordinating conjunction:  His actions were not only irresponsible, but they were also probably illegal.
> Use a semicolon:  His actions were not only irresponsible; they were also probably illegal.
>
Recast as a simple sentence with a compound adjective:  His actions were not only irresponsible but also probably illegal. (No comma is needed.)

4.  Computers are very useful, they enable us to perform complex tasks in a relatively short time.
This is (or should be) an obvious case of running two complete thoughts together with only a comma.  Some possible corrections

> Use a semicolon:  Computers are very useful; they enable us to perform complex tasks in a relatively short time.
>
Subordinate the second clause (create a complex sentence):  Computers are very useful because they enable us to perform complex tasks in a relatively short time.  (No comma is needed before the closing dependent clause.)
> Rearrange and revise the sentence into a complex sentence with the dependent clause first:  Because computers enable us to perform complex tasks in a relatively short time, they are very useful.
>
Convert the sentence to a simple sentence with a participial phrase at the end:  Computers are very useful, enabling us to perform complex tasks in a relatively short time.

5.  We always indulge in some extravagance over the holidays, for example, last year we bought a plasma TV set.
When "for example" introduces an independent clause, that clause should not be grafted onto the previous sentence by only a comma.  Some possible corrections
> Use a semicolon: 
We always indulge in some extravagance over the holidays; for example, last year we bought a plasma TV set.
>
Restructure and rephrase:  We always indulge in some extravagance over the holidays, such as the plasma TV set that we bought last year.

In all cases where we corrected the comma splice by changing the comma to a semicolon, we could also have created two sentences by using a period and a capital letter.

In summary, some of the ways to correct a comma splice are:

  • Change the comma to a semicolon.
  • Insert a coordinating conjunction after the comma.
  • Make one of the clauses subordinate.
  • Rephrase the sentence in a different way, perhaps making it a simple sentence.
  • Use a period and capital letter to create two sentences.