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center for writing | student writing support | grammar | run-on sentences

Run-on sentences

Problem

A run-on sentence occurs when two or more independent clauses are not joined correctly. An independent clause is a group of words that can stand alone as a sentence, as in, The dog runs. Your writing may be confusing or unclear if independent clauses are joined incorrectly.

There are two types of run-on sentences: fused sentences and comma splices.

A fused sentence occurs when independent clauses (indicated here with underlining) run together with no marks of punctuation or coordinating conjunctions to separate them.

fused sentence
My professor read my paper she said it was excellent.

A comma splice occurs when two or more independent clauses are joined only by a comma.

comma splice
My cat meowed angrily, I knew she wanted food.

Solution

Revise run-on sentences in one of four ways:

Use a comma and a coordinating conjunction (and, but, yet, so, or, nor, for).

When you join two independent clauses with a coordinating conjunction, place a comma before the coordinating conjunction.

run-on (fused sentence)
My professor read my paper she said it was excellent.

run-on (comma splice)
My professor read my paper, she said it was excellent.

correction (comma plus coordinating conjunction)
My professor read my paper, and she said it was excellent.

Use a semicolon (or, in some cases, a colon or a dash).

You can use a semicolon alone or with a transitional expression (e.g., however, at any rate, in contrast, as a result, etc.). Remember to put a comma after a transitional expression. That won't create a comma splice: a transitional expression is not an independent clause.

run-on (fused sentence)
My cat meowed angrily I knew she wanted food.

run-on (comma splice)
My cat meowed angrily, I knew she wanted food.

correction (semicolon)
My cat meowed angrily; I knew she wanted food.

correction (semicolon plus transitional expression followed by a comma)
My cat meowed angrily; therefore, I knew she wanted food.

Separate the independent clauses into sentences.

This is an especially good technique when one of the independent clauses is very long.

run-ons (comma splices)
It seemed to Wanda that her daughter had more than enough crayons, they were strewn across the bedroom floor, and some of them were broken, worse still, someone had used the stub of a red crayon to mark a sinister smiley face on the wall.

correction (separate sentences)
It seemed to Wanda that her daughter had more than enough crayons. They were strewn across the bedroom floor, and some of them were broken. Worse still, someone had used the stub of a red crayon to mark a sinister smiley face on the wall.

Restructure the sentence by subordinating one of the clauses.

You can subordinate a clause if one of the independent clauses seems less important than the other. Here are a few examples in which one of the clauses has been subordinated (indicated here by underlining). Note that a subordinated clause is no longer independent—it cannot stand on its own as a sentence.

run-on (comma splice)
The largest tree by volume in the world is the General Sherman Sequoia, it is a little over 52,500 cubic feet.

correction (subordinating the end of the sentence)
The largest tree by volume in the world is the General Sherman Sequoia, which is a little over 52,500 cubic feet.

run-on (comma splice)
Toni Morrison is a professor at Princeton University, she wrote the novel The Bluest Eye.

correction (subordinating the middle of the sentence)
Toni Morrison, a professor at Princeton University, wrote The Bluest Eye.           

run-on (comma splice)
I told my roommate I would be late, she still locked me out.

correction (subordinating the beginning of the sentence)
Although I told my roommate I would be late, she still locked me out.

run-on (fused sentence)
I told the children I would read to them they said they wanted to sit by me so they could look at the pictures.

correction (subordinating the beginning of the sentence)
When I told the children I would read to them, they said they wanted to sit by me so they could look at the pictures.