Comma Splices and Run-On Sentences

Comma splices and run-on sentences are boundary errors: errors caused by not recognizing –and not punctuating properly—the end of one complete thought and the beginning of the next.

Terms to know:

  • An independent clause (also called a main clause) is a group of words that contains a subject and verb and expresses a complete thought. An independent clause can stand alone as a sentence.
  • A dependent clause (also called a subordinate clause) is a group of words that contains a subject and verb but does not express a complete thought. A dependent clause cannot be a sentence. You can spot a dependent clause by looking for a dependent marker (also called a subordinating conjunction, such as after, although, as, as if, because, before, even if, even though, if, in order to, since, though, unless, until, whatever, when, whenever, whether, and while).
  • A run-on sentence incorrectly runs together two independent clauses without a connecting word or punctuation. (This error is sometimes called a fused sentence because the clauses are fused together rather than connected properly.)
  • A comma splice incorrectly joins together (splices) two independent clauses with just a comma.

Both errors may be corrected in any of these 5 ways:

1. Make two separate sentences.

  • The tsunami hit without warning. Thousands were killed.

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

The tsunami hit without warning, and thousands were killed.

3. Use a semicolon. (Use this option when the two clauses express closely related ideas, often in parallel structures.)

  • The tsunami hit without warning; thousands were killed.

4. Use a semicolon and a conjunctive adverb (an independent connector word, such as also, consequently, furthermore, however, moreover, nevertheless, and therefore.) This option helps you to express the relationship between the ideas in the two clauses. Note that the connector word may appear anywhere in the second clause.

  • The tsunami hit without warning; consequently, thousands were killed.
  • The tsunami hit without warning; thousands were killed, consequently.

5. Make one clause into a dependent clause. This option expresses the relationship between the two ideas, highlighting the idea the writer wishes to emphasize in the independent clause.

  • When the tsunami hit without warning, thousands were killed.