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The dos and don'ts of commas

(Side note: If you have a bone to pick with how I punctuated this blog post title, I’ll redirect you here.)

I have a love-hate relationship with commas. I love commas; I was taught to use a comma whenever there would be a natural pause in conversation, so an excess of commas makes a text seem more casual and conversational to me. I hate commas; the rules that guide them are messy, overlapping, and contradictory.

Understanding commas requires some knowledge of other grammatical forms, such as adverbs and conjunctions. This blog post presents some of the basics of commas with (maybe somewhat oversimplified) information on other relevant grammar.

There are a few foundational rules that govern the basics of when to use a comma (or when not to):

Use commas to combine two independent clauses joined by a coordinating conjunction.

Independent clauses are basically groups of words that can stand on their own (like a sentence). An easy way to test if something is an independent clause is to separate it from the rest of the sentence to see if it makes sense on its own.

For example: “The shirt lay on top of the bed, but it was covered by the duvet cover.”

Is the italicized section an independent clause? Yes! Because it would make sense as a standalone sentence without “but it was covered by the duvet cover.” The second part of the sentence—“it was covered by the duvet cover”—is also an independent clause.

To combine these two independent clauses, “but”—a coordinating conjunction—has been used.

There’s also an easy way to remember coordinating conjunctions: FANBOYS.

For

And

Nor

But

Or

Yet

So

Any of these coordinating conjunctions, paired with a comma, can be used to join together two independent clauses.

Use a comma to set off an introductory word, phrase, or clause at the beginning of the sentence.

This rule tends to come somewhat naturally (at least for native speakers).

Some examples:

- “Danielle, do you want to go to Paris?”

- “Oh, I didn’t realize that trains were so fast!”

- “Without her sunglasses, she had to squint under the bright sun.”

Use commas to mark non-restrictive (non-essential) information; don’t use commas to mark restrictive (essential) information.

This rule is much more complicated and confusing; it is also often up for interpretation whether a word, phrase, or clause is restrictive or not, but the inclusion (or omission) of a comma can affect the entire meaning of the sentence.

A non-restrictive element is not essential to the meaning of the sentence. A good way to test this is to remove it from the sentence to see if the meaning of the sentence overall is significantly changed.

For example: “The Parisian sunset, which blazed orange and peach, was enchanting.”

Does removing the italicized section significantly alter the meaning of the sentence? Not really; it adds some color (literally), but it provides additional information that isn’t absolutely necessary to understand the authors meaning. That means that it’s non-restrictive and that it can be set off with commas.

Another example: “The email that she received was shocking.”

Could we remove the italicized section here? No, it would significantly alter the meaning of the sentence overall. Without those three words, the sentence—“The email was shocking.”—misses important information and is much broader than the author intends it to be.

This restrictive/non-restrictive rule can be confusing, and it often becomes much more complicated in sentences with more elements.



Exceptions and specifications:

  1. Use commas to combine two independent clauses joined by a coordinating conjunction (FANBOYS).

  2. Exception: If the independent clauses are short and there is no danger of misreading, the comma may be omitted (editor’s discretion).

  3. Don’t use a comma to combine two independent clauses (comma splice) without a coordinating conjunction; e.g. “She went to the store and he went to the bakery.” (There should be a comma before “and.”)

  4. Don’t use a comma with a coordinating conjunction that joins only words, phrases, or subordinate clauses. Unless the subordinate clause is nonessential (see restrictive/non-restrictive rule).

  5. Don’t include a comma after a coordinating conjunction.

  6. Use a comma after an introductory clause or phrase: a comma tells the reader that the introductory word or phrase has ended and that the main part of the sentence is about to begin.

  7. Participial phrases that function as adjectives describing the noun or pronoun that immediately follows are always followed by a comma; e.g. “Surrounded by the sweet aromas of croissants, I entered the boulangerie.” (“Surrounded by the sweet aromas of croissants” describes “I.”)

  8. The comma may be omitted if the introductory word or phrase is short and there is no danger of misreading; e.g. “In no time we were at our hotel.”

  9. Use commas when addressing someone.

  10. Use a comma to set off transitional (e.g. however, therefore), parenthetical expressions (expressions with additional, not necessary, information), and absolute phrases (phrases that modify the whole sentence).

  11. Between independent clauses in a compound sentence, the transitional expression is preceded by a semicolon and usually followed by a comma.

  12. Don’t use a comma if a transitional expression blends smoothly with the rest of the sentence (e.g. also, at least, certainly, then, etc. may not require commas).

  13. Use commas with nonrestrictive clauses, phrases, etc.

  14. Don’t use a comma to set off restrictive elements.

  15. Optional (this rule is more commonly followed in US English): Use commas before “which,” but not “that” (which = nonrestrictive; that = restrictive).

  16. Use commas with a nonrestrictive appositive; e.g. “The author Susan Sontag is known for her studies on film.” vs. “Susan Sontag, the author, is known for her studies on film.”

  17. Use a comma between coordinate adjectives (adjectives that modify a noun separately) not joined with “and.”

  18. Don’t use a comma between cumulative adjectives (build upon one another), between an adjective and a noun, or between an adverb and an adjective.

  19. Do use a comma with repeated adjectives (e.g. “many, many croissants”).

  20. Use a comma with expressions such as “she said” to set off direct quotations.

  21. Do use a comma with said, replied, asked, wrote, etc.

  22. Don’t (usually) use a comma with that, whether, if, etc.

  23. Use a comma with antithetical elements (something that contradicts the rest of the sentence); e.g. “We were hoping to stay in a luxurious hotel, not this dump of a hostel."

  24. Don’t use commas with word pairs such as “not… but,” “not only… but also,” etc. E.g. “The trip to Paris was going well; we ate not only dozens of croissants, but also several baguettes.” The comma here is unnecessary.

  25. Use commas in a series.

  26. Number of commas (whether or not to use a serial comma) depends on style guide or preference of the author; pick one and stick with it consistently throughout the text.

  27. Be aware that a pair at the end of a series should not be separated by a comma; e.g. “My mother, my sister, and Beyonce and Jay-Z were all in line for the Louvre.”

  28. If using a series comma, omit if an ampersand (&) is used.

  29. Inclusion or omission of series comma can both be confusing; e.g. With serial comma: “My mother, Beyonce, and my sister went to Disney.” Is your mom Beyonce? Or is this a list of three people? (Beyonce could be read as an appositive of “my mother” in this example.)

  30. Don’t use a comma to separate a two-part compound predicate joined by a coordinating conjunction; e.g. “We strolled along the Seine and ate croissants.” Vs. “We strolled along the Seine, and we ate croissants.” (In the first, compound predicate; the second is two independent clauses.)

  31. Although a comma may sometimes be needed to avoid confusion: “We stumbled upon a talented musician playing violin, and watched.” (Without the comma, there could be some confusion about who was watching.)

  32. Don’t use a comma to separate a verb from its subject or object.

  33. Don’t use a comma after after “such as,” “like,” or “although.”

  34. Don’t use a comma before parentheses.

  35. Don’t use a comma before the first or after the last item in a series.

  36. Don’t use a comma after a phrase that begins an inverted sentence; e.g. “At the bottom of the Eiffel Tower, sat a group of tourists enjoying a bottle of wine.” Remove comma!

  37. Don’t use a comma to separate two consecutive conjunctions with an intervening dependent clause; e.g. “We decided that, if it rained, we would return to the hotel.” First comma isn’t necessary.

  38. Don’t use a comma to set off a concluding adverb clause that it is essential for meaning; e.g. “Don’t visit Paris this summer, unless you have researched local COVID measures.” Remove comma! Imagine what this sentence would be like without the clause following the comma; the meaning of the sentence would be much broader than the author intended.

  39. Both “etc.” and “et al.” should be preceded by a comma, unless “et al.” is only preceded by one name.

I hope this blog post can serve as a guide (both for you and for me) on the basics when struggling with commas.

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