Interruptions: Dashes versus Parentheses versus Commas

Three different punctuation marks battle for the opportunity to mark interruptions in your sentence. Which are you going to use? The answer should depend on the type of interruption and on its relevance to your sentence.

Some interruptions are completely irrelevant to the meaning of the sentence, and you want your reader to actually skip right over them and continue reading your sentence. This kind of interruption is indicated by parentheses. The classic parenthetical interruption is an instruction to the reader to look at a table, figure, bibliographical entry, or appendix for more information. Here are some examples:

Pie charts (see Figure 1) are designed to show the percentage breakdowns of the elements that make up a whole.

Whether the stone appears to travel in a straight line or a parabola is all relative (Einstein, 1950).

Other interruptions are actually part of your sentence, and you do want your reader to read them. The only reason they are considered interruptions is that they could have been left out of your sentence with no loss in clarity. These are signaled by commas. They are often commentary about the sentence or additional description.

The first singer, they all agreed, could actually win the contest. (independent comment)

The first singer, a young man from Alabama, could actually win the contest. (additional description)

The third kind of interruption is a surprise. Not that I am going to surprise you with what the third kind of interruption is—but that the third kind of interruption is literally a surprise to the reader. It is a sudden, unexpected interruption that may be even more important than the content of the rest of the sentence. This kind of interruption is like when your boring sitcom rerun is interrupted by a tornado warning in your area. When you return to your sitcom, everything is different. You don’t care as much about the sitcom as about the information contained in the interruption. Here are some examples:

Jane Smith—did I remember to tell you that she is the one who is making the final decision about whether we receive the $2 million contract?—is on the phone.

The supplies we ordered—the color laser printer, the high-resolution flat-panel monitors, and the upgrade to our Adobe Creative Suite software—will be here sometime this week.

Clearly, there are interruptions, and then there are INTERRUPTIONS. Punctuate them appropriately, and your reader will know exactly how to handle them.