How to use commas: separating nonessential information from the main part of a sentence

Commas are one of the most commonly used punctuation marks. Despite how often we use them, though, it’s not always easy to understand when we should include a comma somewhere in a sentence and when we should leave it out. Although there aren’t hard-and-fast rules that clearly spell out all of the cases where we absolutely need to use a comma, comma usage isn’t arbitrary either. Last week, we talked about using commas to separate the last and second-last items in a list (i.e., the Oxford comma or serial comma). Over the next few weeks, we’ll continue to go over different ways in which commas come into play when writing in English.

One way that we use commas is to separate nonessential information from the main part of a sentence. Nonessential information is information that can be removed from a sentence without changing the meaning of the sentence. For example, let’s imagine that we’re writing about someone named Jessica and we want to tell the reader that Jessica bought concert tickets for her sister, who is named Amanda. If Amanda has only one sister, we would write the sentence like this:

• “Jessica bought the tickets for her sister, Amanda.”

In this sentence, we place a comma between “sister” and “Amanda” to indicate that “Amanda” simply provides more specific information about “sister.” Because Jessica has only one sister, “Amanda” is nonessential information: we could remove “Amanda” from the sentence and still narrow down the recipient of the tickets to one specific person. We wouldn’t necessarily know the name of the person who received the tickets, but we would know that they were for Jessica’s sister. If the reader doesn’t know how many sisters Jessica has, the comma signals to the reader that Jessica has only one sister.

Let’s imagine now that Jessica has three sisters: Amanda, Leah, and Sarah. If we again wanted to tell the reader that Jessica bought concert tickets for Amanda, we would write the example sentence provided above like this:

• “Jessica bought the tickets for her sister Amanda.”

In this case, we leave the comma out because “Amanda” is essential information. Jessica has three sisters, so we need to know the name of the sister to know who the concert tickets were for. Otherwise, we can’t narrow the recipient down to one person. Leaving the comma out signals to the reader that Jessica has multiple sisters and Amanda is one of them.

If your reader knows enough about Jessica to know that Amanda is her sister, you could get around the issue of figuring out whether or not to use a comma by writing “Jessica bought the tickets for Amanda.” If your reader wouldn’t know who Amanda is, though, you may need to keep the sentence the way it is to provide context for the name “Amanda.”

Note that we treat essential and nonessential information in a similar way when it falls in the middle of a sentence instead of at the end. In this case, however, we place commas on both sides of the nonessential information.

• “Jessica called her sister, Amanda, to ask about the concert tickets.” (Jessica has one sister, so “Amanda” is nonessential info.)
• “Jessica called her sister Amanda to ask about the concert tickets.” (Jessica has more than one sister, so “Amanda” is essential info.)

Others types of nonessential information that we use in sentences are introductory words, afterthoughts, and interrupting elements. Introductory words are nonessential words that begin a sentence:

• “To be honest, I don’t know where the tickets are.”

Afterthoughts are nonessential words that come at the end of a sentence:

• “I don’t know where the tickets are, to be honest.”
• “The painting is, in fact, an original.”

Introductory words, afterthoughts, and interrupting elements are considered nonessential information because they can be removed from a sentence without changing the meaning of the sentence. In each of the examples above, removing the underlined words wouldn’t alter the meaning of the sentence; we would still know that the writer doesn’t know where the tickets are or that the painting is an original. The underlined words do provide clues to the reader about how frank the writer is being or how counterintuitive a fact may be, which is why they can still be valuable to include, but they aren’t essential for conveying the meaning of the sentence. For this reason, we place commas after introductory words, before afterthoughts, and around interrupting elements.

Unfortunately, there isn’t a complete list of words that function as nonessential words in a sentence. As you can see from the “Amanda” examples, the same word can function as essential or nonessential information depending on the context. The next time that you’re writing a sentence, though, think about whether there are words at the beginning, at the end, or in the middle that aren’t essential to the meaning of the sentence. If you can remove the words without altering the meaning of the sentence, place commas between these words and the main part of the sentence.

Have any lingering questions about using commas to separate nonessential info in sentences? Leave us a note in our comments section below and we’ll do our best to incorporate your questions into one of our upcoming posts.

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