Punctuation is a support system to enhance the organizational flow of a sentence. Often, it also provides transitional cues, and for clarity, it’s important to make that distinction by using specific punctuation marks. Here are three sentences improved by choosing the correct punctuation from various alternatives.
1. She has seen this happen before, several times in fact.
When a sentence takes an abrupt turn in syntactical flow, as here, the sturdy em dash (usually called simply a dash) should be called in to strengthen the transition; a comma is also required between the primary modifying phrase “several times” and “in fact,” which in turn modifies the previous phrase: “She has seen this happen before—several times, in fact.” (Using a dash in place of what is now the first of two commas also clarifies to the reader that the dash represents a more significant transition than the weaker comma does.)
2. The country has benefited from an influx of young workers—namely undocumented immigrants.
Here, a dash correctly signals an abrupt transition, but the sentence displays the common error of failing to punctuate after the adverb namely. (The equivalent phrases “that is to say” and “to wit” would be supplied with a comma, so for consistency, namely should also.) In this case, a comma would be correct in place of the dash, but as in the previous example, the dash sends a message that it represents the more significant of two punctuation marks: “The country has benefited from an influx of young workers—namely, undocumented immigrants.”
3. He’s sending a message by his actions is what he’s doing.
A grammatically flawed statement such as this should never be published unless the writer is reporting a direct quotation, and even then, the idea can be expressed in a paraphrase. Instead of “‘He’s sending a message by his actions is what he’s doing,’ said Smith,” the writer can report, “Smith said that, by his actions, Jones is sending a message.” (A careful speaker would render the sentence more print friendly by saying, “What he’s doing by his actions is sending a message,” but reporters should not correct the grammar of those they interview.)
If the quotation must be published verbatim, insert a comma before “is what he’s doing” to indicate that this is a tacked-on addendum to the main clause: “He’s sending a message by his actions, is what he’s doing.” Technically, a stronger punctuation mark such as a semicolon or a dash is called for, to suggest that the second part of the sentence is a truncation of an independent clause (“that is what he is doing”), but these marks seem intrusive; a comma is a more subtle marker of a change in the sentence’s syntactical structure.