Commas with Parenthetical Expressions

RULE AA:
Separate parenthetical expressions with commas.

Definition of Parenthetical Expression. These are expressions that do not add essential content for understanding the sentence, such as an off-topic comment or a phrase inserted in a sentence that breaks the flow of the idea. These expressions may be placed in parentheses; hence the name.

Rule AA is something of a catch-all, a grammatical version of “other duties as assigned.” Many phrases and clauses are considered parenthetical expressions, including appositives, direct addresses, interpolated asides, and interjections.

Basically, any expression, description, comment, etc. that interrupts the flow of ideas, that can be moved around in the sentence, and that can be placed in parentheses without confusing the reader needs to be separated from the rest of the sentence with commas.

Sample 12.1.   The new mall, I have heard, will be huge.

In sample 12.1, the parenthetical expression is I have heard. This is not part of the idea being expressed in the sentence. It can be moved to the front or end of the sentence. And it could be placed in parentheses. As such, it is separated from the rest of the sentence with commas, one before and one after. Also, if I had written it at the end of the sentence, I would still need to separate it from the rest of the sentence.

Sample 12.2.   This economic forecast model, compared to other models, shows flat growth.

In sample 12.2, the parenthetical expression is compared to other models. Wherever I put it in the sentence, it will need to be separated by commas.

Sample 12.4.   Compared to other models, this economic forecast model shows flat growth.
Sample 12.5.   This economic forecast model shows flat growth, compared to other models.

Sample 12.4 uses the parenthetical expression as an introductory adverbial phrase (Rule G), and sample 12.5 uses it as a non-grammatical final description (Rule X). Because it is a parenthetical expression, no matter where it is in the sentence, it needs to be separated from the rest of the sentence with commas.


Need help with commas? Get Zen Comma, an instructive reference guide on the 17 major uses and misuses of commas, available in PDF and Kindle formats. Read more about Zen Comma.

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  1. #1 by Jamie Barnes on May 14, 2013 - 12:18 pm

    Here is one sentence that may or may not be okay:
    We can help you set up your email addresses, and configure your FTP program, if you want or need that.
    Here is another. AND THIS IS THE MAIN QUESTION that I have. What to do with a parenthetical expression that is followed by an AND.
    We completely understand what it is like to be starting a new business, or even setting up a personal or non-profit website, and just not be in a position to hire a professional to do the job for you.

  2. #2 by preciseedit on May 14, 2013 - 2:12 pm

    Jamie:
    Regarding the first sentence, “and configure your FTP program” is not a parenthetical expression and does not need commas.This phrase simply provides another action that you can do. The correct sentence is “We can help you set up your email addresses and configure your FTP program, if you want or need that.”

    The second sentence is correct as is. The “and” following the parenthetical expression correctly continues the thought started before the parenthetical expression: “starting a new business…and just not….”

    • #3 by Jamie Barnes on May 14, 2013 - 2:38 pm

      So as far as “Interrupters” are concerned, is there a problem with the next word following the comma being an “and”. My point being that a comma and AND creates a connection between two independent clauses. What if by taking the and off of the second half of the sentence, it is no longer an independent clause? Do we ignore the AND and count it as a dependent clause?

  3. #4 by preciseedit on May 14, 2013 - 2:16 pm

    Jamie: Following up on your first sentence.
    Zen Comma Rule AK states, “Don’t use a comma to separate two parts of a compound predicate.” The comma you placed between “addresses” and “and” breaks that rule. The subject “we” has two actions (i.e., a compound predicate), and the comma between the two actions separates the second action from the subject, which is incorrect.

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