Parenthesis is the strategy of setting a word, phrase, or clause off from a sentence to interject additional information into that statement. Despite the name, parenthesis can be accomplished with a two commas or a pair of dashes as well as with a brace of parentheses. However, several problems can occur when writers attempt to parenthesize: The punctuation employed is not appropriate, the parenthesis is misplaced in the sentence, or what appears to be a parenthetical element is in fact something else. The following sentences illustrate these three problems respectively.
1. He took it from me, stole it, really, years ago.
Really is a parenthesis of “stole it” (a parenthesis can follow rather than interrupt the phrase or clause it supplements), and “stole it, really” is a parenthesis of “He took it from me years ago,” so a hierarchy of punctuation should be employed to clarify the sentence organization. Because dashes are more emphatic than commas, they should assume the major parenthetical role; the comma separating “stole it” and really can remain: “He took it from me—stole it, really—years ago.”
2. Attacks relating to phishing fraud attempts have been very common in recent times (e.g., someone posing as an organization’s CEO emails its CFO to request an urgent payment transfer).
A parenthesis should be directly adjacent to the element of the sentence it pertains to. This parenthesis relates to “attacks relating to fraud attempts,” not to “recent times,” so it should immediately follow the former phrase: “Attacks relating to phishing fraud attempts (e.g., someone posing as an organization’s CEO emails its CFO to request an urgent payment transfer) have been very common in recent times.”
3. But the battle has not been lost—the battlefield keeps changing and continuing to evolve—as one door closes, another is opened.
This sentence is punctuated as if “the battlefield keeps changing and continuing to evolve” is a parenthetical statement interrupting the framing sentence, but the statement that remains when the parenthesis is omitted is “But the battle has not been lost; as one door closes, another is opened,” which makes no sense, because the point of the second clause does not follow from that of the first. However, the statement between the dashes is not parenthetical, and the third clause is an extension of the second one, not the initial one.
The first dash correctly signals that a shift in syntax is imminent (another function of the dash besides parenthesis), but another punctuation mark should replace the second dash so that the two dashes are not misinterpreted as bracketing a parenthetical comment: “But the battle has not been lost: The battlefield keeps changing and continuing to evolve; as one door closes, another is opened.” (Another option is to divide the sentence into two statements, as here: “But the battle has not been lost. The battlefield keeps changing and continuing to evolve; as one door closes, another is opened.” In this case, the second dash can be retained instead of replacing it with a semicolon.)