Proper Punctuation for Parenthetical Phrases

By Mark Nichol

Writers often confuse a sentence that contains a parenthetical phrase starting with a conjunction with one that consists of two independent clauses divided by a conjunction, resulting in improper placement of punctuation. Here are a few examples, with discussion and revisions.

1. “The substance starts off in a higher energy state, and by combining with oxygen, ends up in a lower energy state.”
Remove the optional parenthetical phrase “and by combining with oxygen,” and the resulting grammatically flawed sentence is “The substance starts off in a higher energy state ends up in a lower energy state.” The conjunction and must precede the first comma to produce the valid construction “The substance starts off in a higher energy state and ends up in a lower energy state”; therefore, the correctly punctuated revision is “The substance starts off in a higher energy state and, by combining with oxygen, ends up in a lower energy state.”

If the original sentence read, “The substance starts off in a higher energy state, and when it combines with oxygen, it ends up in a lower energy state,” it would be correct. Here, and begins an independent clause (“and when it combines with oxygen, it ends up in a lower energy state”) rather than preceding a parenthetical phrase (“by combining with oxygen”) that is followed by a resumption of the main clause (“ends up in a lower energy state”).

2. “Then the answer is given in more detail, with a fuller explanation, and where possible, some illuminating and fun trivia.”
When the parenthesis is omitted, the sentence that remains is “Then the answer is given in more detail, with a fuller explanation, some illuminating and fun trivia.” As in the previous example, the conjunction and is incorrectly thrown out with the rest of the phrase. (This construction also makes “with a fuller explanation” look like a parenthesis, too, rather than the beginning of a dependent clause.)

The parenthesis is “where possible,” not “and where possible,” so the second comma must follow, not precede, and: “Then the answer is given in more detail, with a fuller explanation and, where possible, some illuminating and fun trivia.”

3. “Deciduous trees decide to cut and run, or in other words, drop all their leaves at once.”
Other conjunctions can be misplaced, too: Here, or is mistakenly situated in the parenthetical phrase, resulting in the framing sentence “Deciduous trees decide to cut and run drop all their leaves at once.”

In this case, however, a comma is necessary before or as well as after it, even though the second half of the sentence is not an independent clause. The phrase “or, in other words, drop all their leaves at once” is an appositive — an elaboration that restates another word or phrase — to the informal descriptive phrase “cut and run,” so the proper revision is “Deciduous trees decide to cut and run, or, in other words, drop all their leaves at once.” (Without the parenthesis, a verbal nudge that the writer is using an amusing turn of phrase, the sentence reads, “Deciduous trees decide to cut and run, or drop all their leaves at once.”)

Click here to get access to 800+ interactive grammar exercises!


Share


6 Responses to “Proper Punctuation for Parenthetical Phrases”

  • Stephen

    What are your thoughts about commas on either side of a single word? You have used them in the proper revision of example 3 around ‘or’, but in the first two examples you have not used them around ‘and’. In example 1, I agree that they would not be correct, but example 2 is a list. If you use the Oxford comma as standard practice, would it be correct to write example 2 as: “Then the answer is given in more detail, with a fuller explanation, and, where possible, some illuminating and fun trivia.”

  • Matt Gaffney

    This is the first time I’ve ever run across anyone else who knows how to punctuate a compound sentence properly. Kudos! I’ve advocated the solution used in examples one and two for thirty years and have repeatedly been overruled by folks who misunderstand what they learned in fourth-grade English and who ignore logic and sentence flow as if they were Satan’s spawn.

    The only quibble I have is with example three. I think I’d re-edit it to use a simply semicolon. It would read “Deciduous trees decide to cut and run; in other words, drop all their leaves at once.”

    Finally, a sensible understanding and explanation of how to punctuate coordinating conjunctions in the midst of sometimes cumbersome phrases!

  • Mark Nichol

    Stephen:

    The second sentence is not a list. It consists of the main clause “Then the answer is given in more detail” with a two-part expansion, separated by a conjunction, consisting of “with a fuller explanation” and “where possible, some illuminating and fun trivia.” (With a change of one word and deletion of another, this revision alters the sentence into a list: “Then the answer is given with more detail, a fuller explanation, and, where possible, some illuminating and fun trivia.”)

  • Mark Nichol

    Matt:

    Thanks for your note! I wouldn’t use a semicolon in that sentence, because what follows is not an independent clause. A dash would work (“Deciduous trees decide to cut and run—in other words, drop all their leaves at once”), but the transition seems too abrupt.

  • thebluebird11

    @Mark: I guess I’ve been doing it incorrectly forever then, because I’m with Stephen as far as commas on either side of the “and.” I think it is not so much a grammatical issue as a chance to give the reader a second to pause, breathe, process the information, and then move on as you add more information. I think that if someone were speaking these sentences, a natural pause (or a breath) would occur there, and I believe a comma would best reflect that in written form. There, I have thrown in my 2 cents. I guess what I’m asking is if it is really wrong to put that “extra” comma there, or if it’s sort of forgivable.

  • Lisia

    In your alternative version of sentence 1, “The substance starts off in a higher energy state, and when it combines with oxygen, it ends up in a lower energy state,” it appears to me that the “and” introduces an independent clause, as you say, but that the independent clause includes the parenthetical phrase: “when it combines with oxygen”. Is that not the case? Can you please explain the rule that allows the “and” to be included in the parenthetical phrase.

Leave a comment: