Editing, Tips and Tricks

Unpacking CMOS: Commas

Originally published on The Scribe Source blog on June 23, 2020.

Few aspects of grammar are as confusing as the comma. What does it do? Where does it go? As with most grammatical conundrums, The Chicago Manual of Style (CMOS) has all the answers. Let’s see what CMOS has to say about the ever-elusive subject of the comma.

What does the comma do?

According to CMOS, the comma signals a break in the structure of a sentence, a slight pause, or a logical tool used to clarify meaning. Depending on the context of the sentence, there are certain ways to use the comma to clarify and properly organize the sentence (CMOS 6.16).

Independent Clauses vs. Dependent Clauses

What are independent and dependent clauses, and how do commas interact with both?

Independent Clauses (CMOS 6.22–6.23)

CMOS states that independent clauses stand on their own and are joined by conjunctions such as and, but, so, yet, etc. Though the comma can be omitted if the clauses are short enough or closely connected to each other, typically commas are needed to separate two independent clauses. Consider:

He dialed her number, but she didn’t pick up. (The comma separates two independent clauses.)

Dependent Clauses (CMOS 6.24–6.25)

Dependent clauses do not stand on their own as complete sentences and instead need an independent clause to complete it. Dependent clauses that precede an independent clause require a comma. Consider:

Even if he dialed her number, (dependent clause, followed by a comma) there was no guarantee she would pick up. (independent clause)

If a dependent clause follows an independent clause, there is no need for a comma at all. This would occur if the dependent clause and the independent clause from earlier switched places. Consider:

There was no guarantee she would pick up (independent clause, no comma) even if he did dial her number. (dependent clause)

Intervening Clauses (CMOS 6.26)

Sometimes, if a sentence becomes complicated, a dependent clause will interrupt two other clauses. When the dependent clause appears between two clauses joined by a coordinating conjunction so that the conjunctions are next to each other, no comma is needed. Consider:

He walked to the market, but when he got there, the market was closed. (But and when are next to each other, so there is no need to separate them with a comma.)

Serializations and the Oxford Comma (CMOS 6.19)

For a list or series of items in a sentence, a comma is typically used to differentiate between the items. In the case of three or more listed items, a comma (the Oxford comma) should be placed before the conjunction. Consider:

She shopped for fruit, vegetables, and meat.

Sometimes the sentence will continue after listing the objects. In this case, a comma is only added if the context of the sentence requires it. Consider:

She needed fruit, vegetables, and meat to prepare a fantastic dinner. (No comma is necessary after the list.)

Fruit, vegetables, and meat, all found in the local grocery store, were the ingredients for a fantastic dinner. (The comma separates an intervening phrase.)

Participial Phrases (CMOS 6.30)

If your sentence includes a participial phrase, such as an introductory phrase or one that appears in the middle of the sentence, the phrase should be separated from the rest of the sentence, using commas. Consider:

Excited for the play, he drove to the theater early to get good seats. (The comma appears after the introductory participial phrase.)

She bought her ticket for the play, giggling with excitement, and found her seat. (The comma separates the participial phrase in the middle of the sentence.)

If commas still feel daunting, CMOS recommends rephrasing your sentence to clarify the meaning. If you are haunted by the difficulty of a particular clause or sentence or worried about where to place the comma, if anywhere, you can always reword your problem sentence.

Comma usage doesn’t have to be hard or horrifying. As long as you are familiar with the rules and willing to try rewording a tough sentence, the comma will be your friend before you know it!

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