Punctuation with Conjunctions

By Mark Nichol

The rules for punctuating in proximity to simple coordinating conjunctions (and, but, and or) are straightforward, but writers can become confused about when and where to put a comma or other punctuation. Sentences that illustrate the basics, and a discussion of each, follow.

When a conjunction links an independent clause (one that could stand on its own as a sentence) with a dependent clause (one that would form an incomplete sentence), omit internal punctuation: “She went to the pool and took a swim,” or “She went to the pool but did not swim.” (“She went to the pool” is an independent clause; “took a swim” and “did not swim” are dependent.)

When a conjunction links two independent clauses, precede it with a comma: “She went to the pool, and then she took a swim,” or “She went to the pool, but she did not swim.” (“Then she took a swim” and “she did not swim” are independent clauses.) The comma may be omitted for a very short compound sentence such as “She swam and then she ate”; longer sentences, such as the examples given earlier in this paragraph, are often written without internal punctuation, but doing so is not recommended, and for consistency, even brief sentences with two independent clauses should include a comma.

A comma should not follow a conjunction unless it is the first of two commas framing a parenthetical phrase, as in “She went to the pool and, soothed by the cool water, took a swim” and “She went to the pool but, chilled by the cold water, did not swim.” (Said another way, don’t precede a verb with a comma unless the comma closes a parenthetical.) These commas bracket “soothed by the cool water” and “chilled by the cold water,” respectively, which, when omitted, leave the sentences “She went to the pool and took a swim” and “She went to the pool but did not swim,” which do not require internal punctuation.

A pair of em dashes or parentheses can take the place of the two commas: When the parenthesis is abrupt or provocative, use em dashes, as in “She went to the pool and—undeterred by the piranhas—took a swim.” When the interruption is subtle or offered as an aside, use parentheses, as in “She went to the pool and (though she felt tired) took a swim.”

Although older literature, especially that written in British English, can be found that employs both a semicolon and a conjunction to provide a stronger contrast between two independent clauses (“She went to the pool; but she did not swim”), this is now considered incorrect, because the semicolon and the conjunction are redundant to each other. If you use a semicolon, the sentence should be rendered as follows: “She went to the pool; she did not swim.” Use of a comma in place of a semicolon in such a sentence is incorrect; this error is called a comma splice.

Sentences in which or connects clauses should follow the same guidelines: “She went to the pool or the beach,” “She went to the pool, or she went to the beach,” “She went to the pool or, depending on the weather, the beach.”

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9 Responses to “Punctuation with Conjunctions”

  • Ian

    Yes, I do have this now, but not the tricky one you left out. What about two independent clauses with an parenthetical phrase?
    “She went to the pool and, soothed by the cool water, she took a swim.”
    That ought to have three commas:
    “She went to the pool, and, soothed by the cool water, she took a swim.”
    But I understand that convention drops the first or the second. Which one?
    Thanks, Ian

  • Matt Gaffney

    I disagree with defining “She went to the pool and took a swim” and “She went to the pool but did not swim” as complex sentences, i.e., that “took a swim” and “did not swim” are dependent clauses.

    I believe that the subject of “took a swim” and “did not swim” is “she” and that “she” is the so-called implied or understood subject. That being the case, the sentences are compound sentences, not complex sentences; nevertheless, no comma’s required because the compound sentences are very short and because a comma would separate the implied subject (which appears in the first part of the compound sentence) from the predicate in the second half of the compound sentence.

    It would also be valid to consider “She” as the subject of compound verbs (“went” and “took”) and (“went” and “did . . . swim”), respectively. If this argument is followed, then each sentence is a simple sentence with a compound verb, i.e., the subject took two actions.

    Correctly analyzing the first sentence is made more difficult because of the mix of formats. The first would have been better written as “She went to the pool and swam.” I’ve heard the expressions “take a bath/shower,” “take a look,” and “take a walk,” but I’ve never heard “take a swim.” It seems so awkward to me that I think I’ll take a couple of aspirins.

  • Nann Dunne

    I have to agree with Matt on the compound sentence explanation. But everyone I know here in Pennsylvania says “took a swim.” The sentence, “I went to the pool and swam,” sounds comical to me. 🙂 Maybe the difference is regional.

  • Bob Howell

    Just weighing in with some Old School comments:

    1. I agree with almost all of the original analysis and advice on how to punctuate these sentences. Thanks, Mark!

    2. I agree with Matt that “took a swim” and “did not swim” are not dependent clauses (while noting as well that Mark never called those complex sentences). But neither do I think that the first two examples are compound sentences; Matt’s second analysis — that they’re simple sentences with compound verbs — is valid. (Yes, “She” is the understood subject, but the subject must be explicit in the sentence for it to qualify as compound.)

    3. Here’s a complex sentence, beginning with a dependent clause introduced by a subordinating conjunction: “Although she liked piranhas, she did not swim.” (As Mark noted, his linking words are coordinating conjunctions.)

    4. Since the subject of semicolons arose, this might have been the place to note that, if a writer wants to clarify the relationship between the two clauses, a conjunctive adverb may be used: “She went to the pool; however, she did not swim.”

    It’s great to have a forum to discuss these matters with people who care!

  • Matt Gaffney

    @ Bob—I agree that the sentences are not complex sentences; however, since Mark referred to each sentence as comprising an independent clause and a dependent clause, then, by definition, he deemed them complex sentences.

    As I reread my comments in light of subsequent comments, I’m leaning more and more to my second notion that the sentences are simple sentences with compound verbs.

  • Preciseedit

    1 subject + compound predicate = no comma.

  • Festus Abiatar

    The discussion is very informative. When I read Mark’s first analysis, my reaction was exactly the same as Matt’s.

    I further agree with Matt that “since Mark referred to each sentence as comprising an independent clause and a dependent clause, then, by definition, he deemed them complex sentences.”

    Bob made an interesting point that “the subject must be explicit in the sentence for it to qualify as compound.” This is one thing that has always confused me. If I’m to take Bob’s word for it, then my confusion is cleared.

  • Mark Nichol

    Ian:

    I was afraid somebody would ask that, because I belatedly realized I neglected to include that topic.

    Treat “soothed by the cool water” as a dependent clause, not a parenthetical: “She went to the pool, and soothed by the cool water, she took a swim.” (Constituent parts: [independent clause] “She went to the pool” [conjunction] “and” [dependent clause] “soothed by the cool water” [independent clause] “she took a swim.”)

  • Nann Dunne

    Ian, this comma question was brought up in a previous column, in which I was the only one who opted for Strunk and White’s treatment of the situation. I’m gratified to see that others’ thinking now agrees with mine. 🙂

    Strunk and White: “Place a comma before a conjunction introducing an independent clause. … If a dependent clause, or an introductory phrase requiring to be set off by a comma, precedes the second independent clause, no comma is needed after the conjunction. “The situation is perilous, but if we are prepared to act promptly, there is still one chance of escape.”

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