What is a Comma Splice or Run-on Sentence?

Why are they wrong?


I have heard many teachers explain why a "comma splice" is wrong, but it's really like trying to explain why driving on the left side of the road is wrong in the United States. It is a somewhat arbitrary decision, but once made, failing to follow the rule can lead to trouble.

First, let's be clear about what a "comma splice" is. It is simply two distinct sentences that are connected with a comma and nothing else. The following sentences are perfectly correct as two separate sentences.

In the morning, I enjoy a jolting cup of coffee.
In the evening, I prefer a relaxing cup of tea.

It is acceptable and correct to join these sentences with a comma and a coordinating conjunction such as "but."

In the morning, I enjoy a jolting cup of coffee, but in the evening, I prefer a relaxing cup of tea.

A writer might also correctly use a semicolon, a conjunctive adverb such as "conversely" and a comma.

In the morning, I enjoy a jolting cup of coffee; conversely, in the evening, I prefer a relaxing cup of tea.

Confident writers know they can even use the semicolon alone because the two sentences are closely related and parallel in construction.

In the morning, I enjoy a jolting cup of coffee; in the evening, I prefer a relaxing cup of tea.

This is where things get to be somewhat arbitrary. If a writer may correctly use a semicolon with a word, or a semicolon alone, or a comma with a word, why can't the writer use a comma alone?

In the morning, I enjoy a jolting cup of coffee, in the evening, I prefer a relaxing cup of tea.                             ^
                                                              (Comma Splice!)

Why is this wrong?

There are those who offer logical explanations, but I find it much easier to accept it as an arbitrary decision.  It is simply "unacceptable." Just as driving on the left is obviously wrong in the United States and quickly recognized by other drivers as "illegal" (against the law), using a comma to join sentences is easily recognized by other writers as "illiterate" (against the rules of literate writing). As a writer, you simply have to know this and remember this.


Run-On Sentences

On a related note, "run-on" or "run together" sentences result when the writer simply does nothing between sentences -- not even a period.

 

In the morning, I enjoy a jolting cup of coffee in the evening, I prefer a relaxing cup of tea.                           ^
                                                         (Run-On Sentence!)


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