Parenthetical phrasing is often punctuated incorrectly, as shown in the following examples, each of which is followed by a discussion and a revision.
1. That’s why they choose to live in San Francisco proper instead of say a suburb like Daly City.
In this sentence, say is being used as a synonym for the parenthetical phrase “for example,” and like that phrase, it must be set off from the sentence: “That’s why they choose to live in San Francisco proper instead of, say, a suburb like Daly City.”
2. As these companies continue to evolve, a focus on organizational structure and governance framework as well as monitoring, testing, and reporting, become increasingly important.
This sentence consists of three components: a subordinate clause, a main clause, and a parenthetical clause within the main clause. However, the parenthetical clause is not correctly set off from the main clause—a comma must precede “as well as” (the beginning of the parenthetical phrase) to counterbalance the one that follows reporting (the end of the parenthetical phrase): “As these companies continue to evolve, a focus on organizational structure and governance framework, as well as monitoring, testing, and reporting, become increasingly important.”
3. It’s imperative for them to have a longer-term approach to the market, and based on that, make permanent changes to their operations.
The superfluous first comma in this sentence exists on the mistaken presumption that it must be placed there to separate two independent clauses. However, this sentence consists of a single main clause with the parenthetical phrase “based on that,” which should be preceded and followed by a pair of commas, so the first comma must follow, not precede, and: “It’s imperative for them to have a longer-term approach to the market and, based on that, make permanent changes to their operations.”
Compare this sentence, which does consist of two independent clauses correctly separated by a comma and includes a second comma whose function is to set the introductory phrase “at times” off from the rest of the second independent clause: “Decisions have to be based on realistic considerations, and at times, that’s when a third party is helpful.”
Compare it as well to “There have been dozens of bankruptcies so far, and, as Smith mentioned, some have already restructured and exited bankruptcy.” This sentence consists of two independent clauses (separated by the comma between far and and) and the parenthetical phrase “as Smith mentioned,” which is bracketed by two additional commas that have no relation to the first comma.