Welcome back for the last of four sessions about the importance of commas in “Punctuation Saves Lives: Part 4”—this time we’re looking at using commas around extra information in a sentence. Here’s the conundrum I presented at the end of my last blog:
Which sentence is correct: the one without commas or the one with commas?
People who live in glass houses should get dressed in the basement.
People, who live in glass houses, should get dressed in the basement.
If you chose the first one, you’re right. If commas are placed around the information “who live in glass houses,” the sentence would be making a sweeping generality that seems ridiculous. The whole sense of the sentence changes based on whether it contains the commas. In our examples, if we include the commas, we’re saying that all people should get dressed in the basement, a statement that clearly doesn’t seem logical. That isn’t the same message that we get if we remove the commas. The information is essential to the meaning of the sentence because it limits or narrows the noun it’s talking about. Without the commas, the phrase “who live in glass houses” narrows the group of people who should get dressed in the basement: only those who live in glass houses.
When trying to determine if the information is extra or essential, it’s necessary to ask yourself, “Do I want to limit or narrow the person, place, or thing being described?” If you are, then DO NOT use commas. Commas in this setting indicate an extra or non-essential description.
Not every case of whether to use commas is as obvious as the previous one. Here’s a set of examples where the information may or may not need to be set off by commas, depending on what a writer is trying to communicate:
My brother who lives in California has never been to New York.
My brother, who lives in California, has never been to New York.
The first version communicates that the speaker/writer has more than one brother, and that a specific one (the one who lives in California) has never been to New York. The second version of the sentence implies that either the writer/speaker has only one brother, so there is no need to narrow the options or that the writer isn’t concerned about differentiating that brother from his or her other brothers. The information within the commas acts as extra material that doesn’t change the meaning of the sentence. The difference is subtle in this set of examples, and the reader wouldn’t be able to judge one version as being more correct than the other without knowing the writer’s intent. So even when the commas are neither obviously correct nor incorrect, there is a subtle shift in what’s being communicated.
The more often you know why you’re using a comma or any other punctuation mark, the more often you’re in control of your writing and your message. My hope is that you’ll be able to keep these reminders about comma usage in mind when you’re revising your own work, building your confidence as you continue to grow as a writer and communicator!