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Punctuation: Commas

Comma Basics

Commas are punctuation marks with a variety of uses. The following constructions require commas:

  1. Serialized lists. In a list with three or more elements, use commas to separate all of the elements of the series.
    Example: This KAM consists of Breadth, Depth, and Application.
    This punctuation rule is also followed for parallel construction in a series.
  2. Nonessential clauses. Use commas to set off clauses that contain information that is nonessential to the sentence's meaning.
    Example: Walden University, established in 1970, offers many degree programs.
    Note that without the middle clause (established in 1970), the sentence still makes sense (Walden University offers many degree programs). Therefore, the clause is nonessential. For more information, view the page on relative, restrictive, and nonrestrictive clauses.
  3. Compound sentences. Use a comma to separate two independent clauses connected by a coordinating conjunction. A coordinating conjunction is a connecting word such as and, but, or or. For more information, view the page on sentence structure and types of sentences.
    Example: Smith (2001) conducted the research, and Heller (2008) commented on the results.
  4. After a dependent introductory clause, phrase, or word. Use a comma after a dependent introductory clause, phrase, or word.
    Example of introductory clause: If you are using this sentence structure, place a comma after the dependent clause.
     
    Example of introductory phrase: Before completing the interviews, I must obtain Walden University approval.
     
    Example of introductory word: Therefore, I created three research questions.
     
    Example of introductory word: However, further research is needed.
  5. Dates. Use a comma to set off the year in exact dates.
    Example: The hospital's pursuit of Magnet status was successful (R. Jones, personal communication, September 18, 2009).
  6. Citations. Use commas to set off the elements of a citation.
    Example: The research was "inconclusive in its implications" (Sanders, 2009, p. 45).
  7. Introducing quotations (not seamless). Use a comma when an independent clause introduces a quotation but is not seamlessly integrated into it.
    Example: Freud (1900) claimed, "the dreamer...assumes that the dream--even if it does not come from another world--has at all events transported the dreamer into another world" (p. 5).

 

Common Comma Errors

The following constructions do not require commas:

  1. Months. Do not use a comma when referring to a month within a particular year.
    Example: I conducted the study in June 2003.
  2. Complex sentences. Do not use a comma in a sentence that joins an independent clause and a dependent clause with a conjunction (and, or, but).
    Example: Smith (2001) found that results were consistent but also suggested further investigation.
  3. Introducing quotations (seamless). Do not use a comma when an independent clause seamlessly introduces a quotation.
    Example: Freud (1900) claimed that "the dreamer...assumes that the dream--even if it does not come from another world--has at all events transported the dreamer into another world" (p. 5).
  4. Comma splices. A comma splice occurs when two independent clauses (complete sentences) are separated by just a comma.
    Example: Jessica and I went to the movies, we had a good time.

There are many ways to correct the sentence above. Review the information on run-on sentences for examples of correctly joining independent clauses.