A run-on sentence occurs when two or more independent clauses are joined without a punctuation mark or a coordinating conjunction. Run-on sentences are also known as fused sentences.

A comma splice occurs when two or more independent clauses are joined with a comma but without a coordinating conjunction (such as and, or, or but).

Another type of comma splice occurs when a word other than a coordinating conjunction is used with a comma to join two or more independent clauses.

In the preceding sentence, however is a conjunctive adverb, not a coordinating conjunction. There are only seven coordinating conjunctions: and, but, for, nor, or, so, and yet.

Many students have difficulty spotting run-on sentences and comma splices in their own writing. Use the accompanying flowchart to help you identify these types of errors in your sentences.

There are four basic ways to correct a run-on sentence or comma splice. Choose the method that best fits your sentence or intended meaning.

Correct a run-on sentence or comma splice by creating two separate sentences. Make sure each independent clause has the appropriate end punctuation mark — a period, a question mark, or (on rare occasions) an exclamation mark.

When the independent clauses are closely connected in meaning, consider joining them with a semicolon. Note that a coordinating conjunction (such as and, or, or but) is not included when you revise with a semicolon (see 4c).

In the second example, the semicolon joins the two clauses connected by the conjunctive adverb as a result. When two independent clauses are joined by a conjunctive adverb, a semicolon is needed.

Two independent clauses can be joined by using both a comma and a coordinating conjunction (and, but, for, nor, or, so, or yet). The coordinating conjunction indicates how the two clauses are related.

A dependent clause contains a subject and a verb but does not express a complete thought. It must always be linked to an independent clause. You can correct a run-on sentence or a comma splice by adding a subordinating conjunction (such as because or although) to one of the independent clauses, thereby making it a dependent clause. The subordinating conjunction makes the thought incomplete and dependent on the independent clause.

or

You can also correct a run-on sentence or a comma splice by changing one of the independent clauses to a phrase.

or

or

Note: A comma or commas may or may not be needed to separate a phrase from the rest of the sentence, depending on how the phrase affects the meaning of the sentence (see 12e). Here are two more examples that show how to revise run-on sentences and comma splices using subordination.