12 Major Comma Uses Explained

Commas are confusing because they are used in many ways. However, the basic principle to using commas is simple: Use commas to separate clauses and phrases within sentences that have their own meaning.

The “rules” for commas below are broadly, but not universally, accepted. However, a careful writer considers two central issues:

  • Reader understanding and
  • Consistency.

The comma guidelines below will help readers understand your message in many cases. However, even if they are not necessary to improve reader understanding, follow them for consistency. Consistency is a characteristic of professional technical writing.

1. Series

The commas help the reader find each unique item (or group of items) in a series by separating them.

Example: School officials are dismayed by poor grades, low attendance, and high drug use.

2. Joining Sentences

You can join two complete sentences with coordinating conjunctions. (The entire set of coordinating conjunctions is for, and, nor, but, or, yet, and so. Together, these create the acronym FANBOYS.) The comma lets the reader know when one point is complete and the next will begin. This comma use only applies when you have complete sentences on either side of the conjunction.

Example: The screen inverter stopped working, and the motherboard began to smoke.

3. Introductory Descriptions

An introductory description is before the subject and describes the main verb in some way, such as when, where, how, and why. The comma at the end of the description signals the reader that the main point of the sentence is about to begin. For consistency, do this with even short introductory descriptions. In the following example, the introductory description is underlined.

Example: Following the symposium, participants collaborated on projects.

4. Interjections

Technical and academic writing are no places for interjections. However, if you use an interjection, separate it from the rest of the sentence with commas. In the following example, the interjection is underlined.

Example: Hurrah, the project is finally complete.

5. Appositives

An appositive renames or restates the person or thing you just wrote. It is equal and indicates the identical information. Appositives are separated from the rest of the sentence with commas to indicate that the information is a restatement. In the following example, the appositive is underlined.

Example: A Do Not Resuscitate order, a form of advanced directive, is often established during end-of-life care.

6. Asides, Interjected Comments, Parenthetical Expressions

While writing a sentence, you may want to include information that is not directly related to the main point of the sentence. To indicate that you are going “off topic,” and to indicate when you are returning to the main topic, separate the information with commas. If you can put these expressions in parentheses, you can use commas, instead. The information is not essential for understanding the point you are trying to make and, therefore, can be safely separated from the rest of the sentence.

Example: The musical trends of the 20th Century, as determined by a survey of published sheet music, indicates a correlation between tempo and public confidence in the national economy.

7. Providing Examples

When you are providing examples of some fact or concept, you create a form of parenthetical expression. Thus, examples, too, are separated from the rest of the sentence with commas.

Example: Alternative forms of transportation, such as bicycles and roller skates, are common but not popular in suburban areas.

8. Adjective Pairs

When you have two or more adjectives or other descriptions immediately before the word they describe, you may need to separate them with commas. If you can change their order, and if you can put and between them without changing the meaning of the sentence, the adjectives are called coordinate adjectives and need to be separated by a comma. The full explanation is far more technical, but if your adjectives meet these two conditions, you will place the commas correctly. The comma indicates that one adjective does not describe the following adjective in some way but that the adjectives equally describe the thing that follows.

Example: An empowered, supported student will find education exciting.

9. Non-restrictive Phrases and Clauses

A non-restrictive phrase or clause does not tell the reader which thing or person you are describing. Rather, a non-restrictive phrase or clause provides an “off-topic” description that is not necessary to understand the main point of the sentence. Separate all non-restrictive phrases and clauses from the rest of the sentence with commas. If the information is necessary for the reader to know which thing or person you are describing, do not use commas.

Example: The maple tree, which harvesters tap for their sap to make syrup, produces seeds in pairs.

Example: The CEO of Widgets.com, who began his career as a shop clerk, has a net worth of $1 million.

10. Dates

If you include the day, month, and year in the date, put commas around the year. If you do not include the day, you do not need the commas.

Example: On July 1, 2004, the publisher will release the new book series.

11. Final descriptive phrases and clauses

A sentence may end with a final descriptive phrase or clause. If the descriptive phrase or clause relates only to the words immediately prior to the description, you do not need a comma. However, if the description relates to the entire sentence, use a comma to separate it. This shows that the description relates to the entire sentence, not just one part of the sentence. (In the following example, the underlined description relates to the entire information in the main sentence. Without a comma, the sentence would indicate that based on their website notice describes why they postponed the ceremony.)

Example: The city council postponed the ceremony, based on their website notice.

12. Quoted Text

In U.S. English, the final comma or period goes inside the ending quotation mark—even if it looks awkward or is not part of the quoted material.

Example: According to business researchers, election results have a “noticeable effect on stock prices,” and the entire stock market generally “finds a new balance.

Incorrect Comma Placement

Do not use commas in the following places within sentences.

1.   Before or (in either…or expressions), nor (in neither…nor expressions), but also (in not only…but also expressions) expressions, and before the second part of other, similar two-part expressions. Example: “The launch will occur either on Friday [no comma] or on Saturday.”

2.   Between the subject and predicate, unless the subject ends with an expression (such as an appositive) that requires commas. Example: “A substitute for natural wood products shipped from Finland [no comma] expands the market base.”

3.   Between two parts of a compound predicate. Example: “Sound waves can produce heart palpitations in people within the wave cone [no comma] and create pressure on sinus tissues.

4.   Between two objects of a verb. Example: “We use ocean currents to create electricity [no comma] and air currents to generate electromagnetic fields.

This concise comma guide was adapted from the forthcoming Bowman’s Concise Guide to Technical Writing.

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12 responses to “12 Major Comma Uses Explained

  1. Always great to read, particularly as I’m often not sure when to insert a comma or not. (Did I do that right? :)

  2. Thanks for stopping by!

    Yes, you used the comma correctly. I hope you found this comma overview useful. If you’re really, really interested comma usage, you might want to head over to the Zen Comma blog, too.

  3. I get commas and semi-colon usage confused as in this example: “The serious man brought along a knapsack full of gear with him, like usual. Some fruit and yogurt for breakfast later; some water to replenish him along the way; Dostoyevsky and Emerson to get sucked into; his favorite blanket that went with him everywhere; his camera, his walking stick and agenda.”

    What should the punctuation be in this sentence? You don’t have to reply if you don’t want to, I know y’all aren’t my editors! haha :)

  4. Pete–Semicolons are fairly simple. They are used for two purposes.

    First, they are used to connect two independent clauses (complete sentences) without a conjunction. Example: “The author published his book; he waited by the mailbox for the royalty checks to start coming.”

    Second, they are used to separate items in a list if at least one item has its own comma. Example: “The author published his book; waited by the mailbox, with a glossy expression; and crossed his fingers.”

    I would make the following punctuation changes to your example. 1. Put a colon after “like usual.” The colon will prevent the following list from being a sentence fragment and will introduce the list. 2. Change the semicolons to commas. The items in the list don’t have their own commas, so you can use commas to separate them.

  5. Wow, I appreciate that. I’ve been totally stuck and all over the map on colons, semi-colons vs. commas. I’m much obliged.



  6. Right or wrong?Last week’s test says my best friend was the hardest ever.It Depends! In the above example sentence my best friend is probably not a part of the main sentence Last week’s test was the hardest ever and should be separated with commas. Without commas, the reader may get confused and think that the test “says” that the friend was the hardest, while it is the test that was the hardest. Says my best friend serves as a comment, known as a parenthetical element. The correct punctuation would therefore be: Last week’s test, says my best friend, was the hardest ever.

  7. Las Artes-You’re right. It depends.

    Your original sentence is similar to the following example:
    “My grandmother said my friend is pretty.”
    As the sentence is written, my grandmother thinks my friend is pretty. If this is the intended message, this version is correct.

    Now let’s put in commas.
    “My grandmother, said my friend, is pretty.”
    Here, my friend thinks my grandmother is pretty. If this is the intended message, this version is correct. Here, “said my friend” is a parenthetical expression.

    This example shows us that where we put in commas, or where we leave them out, can change the meaning of the sentence.

  8. What about using the word “that”? Off the subject of commas some but the two examples that Las Artes gave read to me like this (if I was editing it myself I mean):

    My best friends says that last week’s test was the hardest ever.
    My friend said that my grandmother is pretty.

    Just curious about both of your thoughts. :)

  9. (my best friend says) haha

  10. Pete: Let’s look at how you revised the sentence “My friend said that my grandmother is pretty.”

    First, you revised the sentence to make it more straightforward. It now begins with the subject, continues immediately to the main verb, and concludes with the object.

      Subject: My friend
      Verb: said
      Object: that my grandmother is pretty.

    This is the S-V-O sentence structure, which is generally the easiest structure for the reader to understand because it answer the central question “Who did what to whom?” The person/thing doing the action (who) is first. The action (did what) is second, and the thing on which the action is performed (to whom) is third.
    The original versions do not follow this pattern and, as a result, seem a bit awkward.
    I wrote about the S-V-O sentence structure quite a bit in the Precise Edit Training Manual and 300 Days of Better Writing, but this brief description here should help explain why I prefer your revision to the original.

    Second (now, finally, to your question!), the word “that” is optional in both of your sentences. Among other uses, “that” is used to turn a phrase or clause into a noun phrase. In your sentences, “that” turns the independent clause “my grandmother is pretty” into a noun phrase [that] you can use as the object of “said.”
    When you use the word “that” to create an object, “that” is generally optional. On the other hand, if the verb has two objects, both noun phrases with “that,” I recommend leaving in “that” to help the reader identify the second object, as follows.
    “My friend said that my grandmother is pretty and that she is blind.”
    If you write this without “that,” the sentence becomes confusing. Who is blind, my friend or my grandmother?
    “My friend said that my grandmother is pretty and she is blind.”
    Without “that,” the reader might not understand that the sentence has two objects because it looks like two independent clauses.

    How’s that for dollar answer to a nickel question?

  11. Tosh Pointo

    Very helpful stuff here — I love it! Still hate commas, though (too many rules!).

  12. Harish Puvvula

    By far the best article/post on comma usage!

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