Run-on sentences

On this page

• How to recognize a run-on
  • Fused run-on
  • Comma splice
  • “And” run-on
• How to correct a run-on
  • Use a period
  • Use a semicolon
  • Use a comma and a conjunction
  • Change one clause into something else
• Additional information

How to recognize a run-on

A run-on sentence is one that contains two or more independent clauses, or simple sentences, that have been run together without a proper connection. (For more information on independent clauses, see our writing tip “Simple sentences”.)

There are three types of run-on:

• the fused run-on
• the comma splice
• the and run-on

Fused run-on

In a fused run-on, two or more independent clauses are run together without any punctuation or joining word between them, as in the example below:

• The power went out last night the lights were off all over the city.

This sentence contains two independent clauses:

• the power went out last night
• the lights were off all over the city

Each clause is a complete thought and can stand alone (that’s why it’s called an independent clause). Putting the two independent clauses together into a single sentence without anything to connect them creates a fused run-on.

Comma splice

Many writers would recognize the example above as wrong but would think they could correct it by adding a comma between the independent clauses:

• The power went out last night, the lights were off all over the city.

But this example shows a second type of run-on known as a comma splice. A comma splice occurs when a writer uses a comma by itself to join independent clauses, without any conjunction (joining word).

Comma splices with conjunctive adverbs

The comma splice is especially common when there is a conjunctive adverb (however, therefore, consequently, etc.) or a similar transitional expression at the beginning of the second clause:

• The power went out last night, therefore, the lights were off all over the city.

Conjunctive adverbs and other transitional expressions do show a link between ideas. (See our writing tips Conjunctive adverbs and Clear communication: Transition words.) But they aren’t conjunctions (joining words), so they can’t be used with a comma to join two sentences. As a result, the example above is still a comma splice.

“And” run-on

To join two independent clauses correctly with a coordinating conjunction (for, and, nor, but, or, yet, so), we need to put a comma at the end of the first clause, before the conjunction. In an and run-on, the comma has been omitted:

• The power went out last night and the lights were off all over the city.

Although this error is called an and run-on (because it most often occurs with and), it can occur with any coordinating conjunction. The example with so below is also an and run-on:

• The power went out last night so the lights were off all over the city.

(For more information on coordinating conjunctions, see our writing tip “Coordinating conjunctions”.)

How to correct a run-on

To correct a run-on sentence, try one of the following solutions.

Use a period

Separate the two independent clauses with a period:

• The power went out last night. The lights were off all over the city.

Use a semicolon

Join the two independent clauses with a semicolon:

• The power went out last night; the lights were off all over the city.

After the semicolon, to improve the flow of ideas, you can also add a conjunctive adverb or other transitional expression, followed by a comma:

• The power went out last night; therefore, the lights were off all over the city.

(For more information on this solution, see the sections “Method 2: Use a semicolon” and “Method 3: Use a semicolon with a transitional expression” in our writing tip “Compound sentences”.)

Use a comma and a conjunction

Join the two independent clauses with a comma and a coordinating conjunction (for, and, nor, but, or, yet, so):

• The power went out last night, and the lights were off all over the city.
• The power went out last night, so the lights were off all over the city.

(For more information on this solution, see the section “Method 1: Use a comma and a coordinating conjunction” in our writing tip “Compound sentences”.)

Change one clause into something else

Finally, you can fix a run-on by changing one of the clauses into a different kind of structure.

For example, you could make one of the independent clauses into a dependent clause:

• When the power went out last night, the lights were off all over the city.

(For more information on this solution, see our writing tip “Complex sentences”.)

Another option would be to make one of the clauses into a phrase:

• During last night’s power outage, the lights were off all over the city. [first clause made into prepositional phrase]
• The power went out last night, leaving the entire city in darkness. [second clause made into participle phrase]

(For more information on phrases, see our writing tips Prepositional phrase and Participle, participle phrase.)

Additional information

• Simple sentences
• Conjunctive adverbs
• Clear communication: Transition words
• Coordinating conjunctions
• Compound sentences
• Complex sentences
• Prepositional phrase
• Participle, participle phrase