By the end of this section, you will be able to:
- Distinguish between essential and nonessential information in sentences.
- Use commas for clearer, more effective sentences.
A comma is a mark of separation. It alerts readers to a brief pause or pauses within a sentence that is part of your analytical report.
Nonessential and Essential information
Nonessential information refers to information within a sentence that is not necessary for the reader to understand its meaning. Essential information refers to information within a sentence that is necessary for the reader to understand its meaning.
Placing commas around a word or group of words within a sentence usually indicates that the information is not necessary for readers to understand the sentence’s meaning. In the example below, the underlined words refer to and explain the phrase current math curriculum, but they can be removed without changing the meaning of the sentence: the math curriculum currently in use isn’t meeting current needs. The information is interesting and perhaps useful, but it is “extra” and does not change the basic meaning of the sentence.
The current math curriculum, which was adopted by the school district 10 years ago, no longer meets the needs of the students.
Certain words in a sentence are often necessary for readers to understand its meaning. In the example below, the word current was removed from between the words The and math and replaced by the underlined words that tell readers which curriculum no longer meets students’ needs. It is essential because without it, confusion may arise about which math curriculum no longer meets students’ needs.
The math curriculum that the district adopted 10 years ago no longer meets the needs of the students.
To Comma or Not to Comma?
Place commas around nonessential information, but not around essential information. You can test whether information is nonessential by removing the information. If the meaning of the sentence is unchanged, the information is nonessential. If the meaning becomes too general or changes in any way, the information is essential. Often, nonessential information is introduced with the word which and essential information with that.
Place Commas around Nonessential Information
Place commas around information that is not essential to the meaning of a sentence, as illustrated in the following sentences:
- The entire math department, which consists of 16 teachers and 7 staff members, has requested a review of the curriculum.
- The department chair, who has led the math department for 11 years, has agreed to the teachers’ request.
- The curriculum will become effective in June, when the school year is finished.
Do Not Place Commas around Essential Information
Do not place commas around information that is essential to the meaning of a sentence, as illustrated in the following sentences:
- According to the department chair, the math curriculum needs to focus on skills that students need after high school graduation.
- The math teachers who teach Algebra 1 and Algebra 2 have requested a review of the curriculum.
- The teachers are concerned that students are not retaining what they have learned.
- The department has consulted the curriculum expert Malcolm Green.
See Punctuation for more on commas.
Practice Using Commas
Read each of the following sentences. Decide whether the underlined portion of each sentence is nonessential or essential. Place commas before, after, or around the nonessential information as appropriate.
- The department has consulted the curriculum expert Malcolm Green whose textbook is widely used.
- Two members of the math department Janelle Brady and Tye Lavalle are retiring next year.
- The textbooks that are now in use are outdated.
- Students have given feedback on the online classes that have replaced in-person classes.
- The math department now offers more evening classes which attract more students and fewer summer classes.
- Several instructors who teach math also teach computer science classes.