Coordination of Conjunctions and Punctuation

When a conjunction is inserted into a sentence to separate two cumulative elements of the sentence, where commas, if any, are correctly positioned depends on the syntactical structure of the sentence regardless of whether a parenthetical phrase complicates the sentence. In each sentence with parenthesis below, the punctuation is not appropriate for the syntax. Discussion after each example explains the problem, and a revision provides a solution.

1. That debate could place everything on the table and, for that reason, significant tax reform in 2017 may prove challenging to achieve.

This sentence consists of two independent clauses interrupted by the modifying phrase “for that reason” (which introduces the second clause). Without that phrase, the sentence would read, “That debate could place everything on the table, and significant tax reform in 2017 may prove challenging to achieve.” In the original sentence, “for that reason” is treated as a parenthetical phrase and is therefore bracketed by commas, but it is an introductory phrase, and so only the following comma is necessary: “That debate could place everything on the table, and for that reason, significant tax reform in 2017 may prove challenging to achieve.”

2. The business recently acted on the recommendation, and early on in its transformation process, has already generated valuable time and money-saving efficiencies.

Here, the second part of the sentence shares the subject “the business,” so that section of the sentence is not an independent clause. The root sentence is “The business recently acted on the recommendation and has already generated valuable time and money-saving efficiencies.” Therefore, the punctuation should frame the parenthesis: “The business recently acted on the recommendation and, early on in its transformation process, has already generated valuable time and money-saving efficiencies.”

3. We observed several cases in which models were built solely based on a quantitative approach, and, as a result, generated poor model fit and model performance.

This example has the same syntactical structure as the previous one but includes both a comma intended to separate independent clauses and a pair of commas to set off the parenthetical. However, the part of the sentence following the parenthetical is not an independent clause, so the first comma is an error: “We observed several cases in which models were built solely based on a quantitative approach and, as a result, generated poor model fit and model performance.”