run-on sentence (grammar and usage)

Glossary of Grammatical and Rhetorical Terms

run-on sentence
See Five Ways of Correcting Run-on Sentences (below). (Getty Images)


In prescriptive grammar, a run-on sentence is two independent clauses that have been run together without an appropriate conjunction and/or mark of punctuation between them. Put another way, a run-on is a compound sentence that has been incorrectly coordinated and/or punctuated. Also called a run-together sentence.

Run-on sentences aren't always excessively long sentences, but they can be confusing to readers because they tend to express more than one main idea without making clear connections.

(See sentence length.)

Usage guides commonly identify two kinds of run-on sentences: fused sentences and comma splices.


Five Ways of Correcting Run-on Sentences

  1. Run-on Sentences:
    • Adam is a sweet boy he really loves animals.
    • Adam is a sweet boy, he really loves animals.
    To correct a run-on sentence, make it into two simple sentences. Put a period at the end of the first subject and verb group. Start the second sentence with a capital letter.
    Correct Sentences:
    Adam is a sweet boy. He really loves animals.
    (Jill Singleton, Writers at Work: The Paragraph. Cambridge University Press, 2005)
  2. Sometimes two sentences are very closely related in meaning and full end-stop punctuation may seem too strong. A semicolon can then be used to divide the two sentences. . . .
    Run-on: It was a beautiful day there was not a cloud in the sky.
    Correct: It was a beautiful day; there was not a cloud in the sky.
    (Phil Pine, Master the SAT 2008. Peterson's, 2007)
  1. A run-on sentence can sometimes be prevented by using a comma and joining word (coordinate conjunction) to join sentences together.
    Wrong: John went to the movies x Sue stayed home.
    Correct: John went to the movies, and Sue stayed home.
    (Christopher Smith et al., How to Prepare for the GED. Barron's, 2004)
  1. Sometimes you can reduce two spliced or fused clauses to a single independent clause that is more direct and concise:
    Comma Splice: A large part of my mail is advertisements, most of the rest is bills.
    Correct: A large part of my mail is advertisements and bills.
    (Andrea A. Lunsford, The St. Martin's Handbook, 6th ed. Bedford/St. Martin's, 2008)
  2. "[Another way to correct a run-on sentence is to] change the run-on to a complex sentence by placing a subordinating conjunction before one of the clauses:
    Run-on: I don't play tennis well I have a poor backhand.
    Correct: I don't play tennis well because I have a poor backhand.
    (P. Choy and D.G. Clarke, Basic Grammar and Usage. Cengage, 2005)

Examples and Observations

  • Comma Splices and Fused Sentences
    "A comma splice is a sentence error in which two independent clauses are incorrectly separated by a comma instead of a period. A fused sentence is an error in which two sentences are run together without a punctuation mark between them. Comma splices and fused sentences are types of run-on sentences because they run together sentences that should be separated.
    Comma Splice: Beethoven was not born deaf, he lost his hearing gradually.
    Revised: Beethoven was not born deaf. He lost his hearing gradually.
    Fused Sentence: Beethoven was not born deaf he lost his hearing gradually.
    Revised: Beethoven was not born deaf; he lost his hearing gradually."
    (Robert DiYanni and Pat C. Hoy II, The Scribner Handbook for Writers, 3rd ed. Allyn and Bacon, 2001)

  • Run-ons and Comma Splices
    "The presence or absence of a comma—and therefore the distinction between a run-on sentence and a comma splice—isn't usually noteworthy. So most writers class the two problems together as run-on sentences.

    "But the distinction can be helpful in differentiating between the wholly unacceptable (true run-on sentences) and the usually-but-not-always unacceptable (comma splices). That is, most usage authorities accept comma splices when (1) the clauses are short and closely related, (2) there is no danger of a miscue, and (3) the context is informal. Thus: 'Jane likes him, I don't.' But even when all three criteria are met, some readers are likely to object. And in any event a dash seems preferable to a comma in a sentence like that one."
    (Bryan A. Garner, The Oxford Dictionary of American Usage and Style. Oxford University Press, 2000)