When a sentence includes a form of parenthesis—a word, phrase, or clause framed by a pair of commas, dashes, or parentheses—writers must take care that the statement surrounding the interjection is structurally valid so that if the optional parenthesis is omitted, the remaining wording is still coherent and thus the parenthesis makes sense grammatically. To test whether the sentence’s composition is complete, temporarily omit the interjection, then repair any syntactical and grammatical issues that manifest themselves before reinstating (or restating) the parenthesis. The following sentences are flawed in construction, and the discussion and revision that follows each resolves the problem.
1. He is considered to be one of, if not the, deadliest assassin in the empire.
This sentence, without the parenthesis, is “He is considered to be one of deadliest assassin in the empire.” This faulty construction demonstrates that the article the must appear in the main clause before the interjection to form a complete sentence, and assassin must be in plural form to correspond with the modifying phrase “one of the” (“He is considered to be one of the deadliest assassins in the empire”); in addition, a repetition of deadliest must be inserted into the parenthesis to form a complete thought: “He is considered one of the deadliest assassins, if not the deadliest, in the empire.” (The extraneous “to be” has been deleted as well.)
2. There is little doubt he will be regarded as one of the worst, if not the worst, governors in the state’s history.
The flaw in this sentence is similar to that of the previous example, though in this case, correction of the error is simpler—the main clause is valid, but the plural form governors is at odds with the parenthetical phrase “if not the worst.” To rectify the error, simply relocate that phrase to the end of the sentence to transform it from a parenthetical to a subordinate clause, thereby disassociating it from governors, the singular form of which is now implied after the phrase: “There is little doubt he will be regarded as one of the worst governors in the state’s history, if not the worst.” (Another possible solution is to transpose the two complementary phrases: “There is little doubt he will be regarded as, if not the worst governor in the state’s history, one of the worst.”)
3. Effective risk management can help predict—and prevent—major implementation problems from occurring.
In this case, the wording that remains after the parenthesis is excised—“Effective risk management can help predict major implementation problems from occurring”—is syntactically flawed, because “from occurring” modifies prevent but not predict. For the sentence to make sense, that phrase should be inserted into the interjection: “Effective risk management can help predict—and prevent from occurring—major implementation problems.” Better yet, integrate the interjection (with a pronoun standing in for a repeat of “major implementation problems”) into the main clause: “Effective risk management can help predict major implementation problems and prevent them from occurring.”
4. This has not (and should not) prevent smart companies from taking advantage of innovation.
With the parenthesis in this sentence removed, the remaining statement is “This has not prevent smart companies from taking advantage of innovation.” Because “has not” and “should not” must be accompanied by differing forms of prevent, both forms of the verb, one in the main clause and one in the parenthesis, should be employed: “This has not prevented (and should not prevent) smart companies from taking advantage of innovation.”
Note that, as is often the case, the three forms of punctuation are interchangeable, although their functions vary slightly: Commas are neutral, parentheses suggest that the information is incidental, and dashes signal information that is divergent or unexpected.
5. One could argue that regulators are neither responsible for, nor able to, change a financial institution’s culture.
Here, as in the previous example, the parenthetical is compatible with the phrase that follows it but not the one preceding it, and the error can be tested by temporarily omitting the parenthetical to discover that the base sentence is grammatically incorrect. In the resulting sentence, “One could argue that regulators are neither responsible for change a financial institution’s culture,” change should be changing. However, change is correct when associated with “nor able to,” so when the parenthetical is returned to the sentence, both forms of the verb must be included, one in the main clause and one in the parenthetical: “One could argue that regulators are neither responsible for changing, nor able to change, a financial institution’s culture.”