What Are Run-on Sentences?

Absence of Conjunctions or Punctuation Between Independent Clauses

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

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

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 between the two.

Usage guides commonly identify two kinds of run-on sentences: fused sentences and comma splices. In either case, there are five common ways of correcting a run-on sentence: making the independent clauses two simple sentences separated by a period; adding a semicolon; using a comma and a coordinating conjunction word; reducing the two to a single independent clause; or changing the sentence into a complex sentence by adding a subordinating conjunction before one of the clauses.

Comma Splices and Fused Sentences

Sometimes, run-on sentences occur even when a comma is present between independent clauses because of the omission of joining words and phrases. This type of error is called a comma splice and typically should be separated by either a semicolon or a period instead.

Interestingly, Bryan A. Garner's "The Oxford Dictionary of American Usage and Style" notes that while there is a distinction between run-on sentences and comma splices, it isn't typically noteworthy.

However, Garner also notes "the distinction can be helpful in differentiating between the wholly unacceptable (true run-on sentences) and the usually-but-not-always unacceptable (comma splices)." 

As a result, comma splices may sometimes be regarded as acceptable in certain situations; fused sentences, on the other hand, occur when there is an error in which two sentences "are run together without a punctuation mark between them," according to Robert DiYanni and Pat Hoy II's "The Scribner Handbook for Writers." Fused sentences are never accepted as grammatically acceptable.

Five Ways of Correcting Run-on Sentences

Academic writing requires grammatical accuracy in order for the work to be taken seriously; as a result, it is important for writers to eliminate run-on sentences in order to convey a professional tone and style. Fortunately, there are five common ways in which grammarians recommend fixing run-on sentences:

  1. Make two simple sentences of the run-on sentence.
  2. Add a semicolon to divide the two sentences to imply and/or between them.
  3. Add a comma and joining word to link the two sentences.
  4. Reduce the two spliced sentences to one cohesive sentence.
  5. Place a subordinating conjunction before one of the clauses.

As an example, take the incorrect run-on sentence "Cory loves food he has his own blog about restaurants." To correct this, one might add a period after "food" and capitalize the word "he" to form two simple sentences or add a semicolon to imply the word "and" between "food" and "he."

Alternatively, one might add a comma and the word "and" to join the two sentences together or reduce the sentence to "Cory loves food and even has his own food blog" to form the two clauses into a single independent clause. Finally, one can add a subordinating conjunction like "because" to one of the clauses to form a complex sentence like "Because Cory loves food, he has his own food blog."