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Grammar and Mechanics: Run-On Sentences and Sentence Fragments

Run-On Sentences

A run-on sentence occurs when two or more independent clauses (also known as complete sentences) are connected improperly.

Key: yellow, bold = Sentence 1; green, italics = Sentence 2; blue, underlined = conjunction; pink, regular font = dependent clause

ExampleParticipants could leave the study at any time they needed to indicate their preference.

There are two complete sentences in the above example:

  • Sentence 1: Participants could leave the study at any time.
  • Sentence 2: They needed to indicate their preference.

One common type of run-on sentence is a comma splice. A comma splice occurs when two independent clauses are joined with just a comma.

Example of a comma splice: The United States is facing an obesity epidemic, excess weight contributes to other health conditions, including diabetes, asthma, and cardiovascular disease.
  • Sentence 1: The United States is facing an obesity epidemic.
  • Sentence 2: Excess weight contributes to other health conditions, including diabetes, asthma, and cardiovascular disease.

Some comma splices occur when a writer attempts to use a transitional expression between two independent clauses.

Example of a comma splice: The results of the study were inconclusive, therefore more research needs to be done on the topic.
  • Sentence 1: The results of the study were inconclusive
  • Transitional expression (conjunctive adverb): therefore
  • Sentence 2: More research needs to be done on the topic

To fix this type of comma splice, one option is to use a semicolon before the transitional expression and add a comma after it. See more examples of this on the semicolon page.

Revision: The results of the study were inconclusive; therefore, more research needs to be done on the topic.

Correcting Run-On Sentences

A run-on sentence can be fixed by either separating or connecting the independent clauses correctly. There are several ways to do so:

  1. Use a period. The easiest way to fix a run-on is to split the sentence into smaller sentences using a period. This revision works especially well with longer sentences. Check to make sure that this solution does not result in short, choppy sentences.
    Revision example: Participants could leave the study at any time. They needed to indicate their preference.
  2. Use a semicolon. Inserting a semicolon between independent clauses creates a grammatically correct sentence. Using a semicolon is a stylistic choice that establishes a close relationship between the two sentences.
    Revision example: Participants could leave the study at any time; they needed to indicate their preference.
  3. Use a comma and a coordinating conjunction. A comma, paired with a coordinating conjunction (such as and, but, or or), corrects a run-on sentence. This method emphasizes the relationship between the two clauses.
    Revision exampleParticipants could leave the study at any time, but they needed to indicate their preference.
  4. Use a subordinating conjunction. Turn one of the independent clauses into a dependent clause. A subordinating conjunction (such as because, unless, and although) connects two clauses to create a complex sentence. This option works to cement the relationship between the two parts of the sentence and may improve the flow of the clauses.
    Example: By indicating their preference, participants could leave the study at any time.

There are many ways to revise a run-on sentence; remember that maintaining sentence variety helps to keep the writing clear and interesting for readers.

Sentence Fragments

A sentence fragment is a string of words that does not form a complete sentence. This occurs when a necessary component of a complete sentence, such as a subject (usually a noun) or a predicate (verb or verb phrase), is missing and/or when the sentence does not express a complete idea.

Key: yellow, bold= subject; green, italics = predicate; pink, regular font = dependent clause

 

Example of a fragment with a missing subject: Employs strategies to encourage classroom participation, including using small groups and clarifying expectations.

The sentence above is a fragment because there is no subject (Who employs these strategies?). Fragments can be corrected by identifying the missing element and including it.

Possible revision: The teacher employs strategies to encourage classroom participation, including using small groups and clarifying expectations.

 

Example of a fragment with a missing predicate, or action: Completing a more complex examination of the gene-environment interaction model postulated by Bronfenbrenner (1994) and the negative cognitive appraisal theory.

Notice here that although the sentence is quite long, it still contains no action (What is the action or result of completing this examination?).

Possible revision: Completing a more comprehensive examination of the gene-environment interaction model postulated by Bronfenbrenner (1994) and the negative cognitive appraisal theory would allow future researchers to find effective treatment options.

 

Example of a fragment expressing an incomplete idea: Whereas gender is considered one’s sexual orientation based on the individual’s external social and psychological patterns of behavior and self-perception.
Possible revision: Sex means the biological differences between male and female whereas gender is considered one’s sexual orientation based on the individual’s external social and psychological patterns of behavior and self-perception.