The Comma Part 6: An overview of when and how to use a comma

The primary purpose of punctuation is to ensure the clarity and readability of writing. Punctuation clarifies sentence structure, separating some words and grouping others. It adds meaning to written words and guides the understanding of readers as they move through sentences. Often people advise that commas are used as a “pause” or a “breath” in a sentence, but that’s not really all that helpful in providing technical rules or guidelines. And there are, in fact, some fairly technical rules and guidelines when it comes to comma usage.




To separate words, phrases, and clauses in a series. When using a comma for a series of words, the last comma you use is known as the Oxford comma and can change the meaning or relationship of the last two items in the list.

  1. For words:  Boccaccio’s tales have inspired plays, films, operas, and paintings.
  2. For phrases:  Alexander the Great established a system of fortified cities, reorganised the military, and built a fleet of warships.
  3. For clauses:  In the Great Depression, millions lost their jobs, businesses failed, and charitable institutions closed their doors.


Between coordinate adjectives – that is, adjectives that separately modify the same noun. Example: Critics praise the novel’s unaffected, unadorned style.



Before a coordinating conjunction (and, but, for, nor, or, yet, or so) joining independent clauses in one sentence. Example: The poem is ironic, for the poet’s meaning contrasts her words.



To set off a parenthetical comment, or an aside, if it is brief and closely related to the rest of the sentence. Example: The first year university, for example, is a very busy year.



To set off a nonrestrictive modifier – that is a descriptive word/phrase that is not essential to the meaning of the sentence, i.e. it could potentially be dropped without changing the main sentence. Example: J K Rowling, the author of the Harry Potter books, will offer an online reading tonight.


Here are some other examples from our friends over at ProWritingAid:




Sometimes, your instructor might point out that you’ve used a comma splice in your essay. So what is it and how can you resolve it? Here are some quick articles to show you how to fix it. 


1. What is a comma splice?

2. Use a semi-colon or colon to fix a comma splice.

3. Use a coordinate conjunction.

4. Use a subordinate clause


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