uw-madison writing center writer's handbook

Use the guidelines below to learn how to use commas effectively in your writing.

Definitions and examples of non-restrictive vs. restrictive modifiers
Further examples
Self-test sentences and answers

Using commas to punctuate restrictive and non-restrictive modifiers

Use commas to set off non-restrictive modifiers.

Do not use commas to set off restrictive modifiers.

Non-restrictive vs. restrictive modifiers

A non-restrictive modifier adds information that is not essential to our understanding of the sentence; if we remove it from the sentence, the basic meaning of the sentence does not change.

A restrictive modifier identifies, or limits the reference of, the noun it modifies.

The table below illustrates these definitions.

Type of modifier

Example

Explanation

Non-restrictive

The statue of his mother by Joseph Smith, dated 1894, sold for over a million dollars.

The date of Joseph Smith's statue can be removed from the sentence without altering its meaning:

The statue of his mother by Joseph Smith sold for over a million dollars.

Restrictive

The painting dated 1894 is a forgery; the one dated 1892 is genuine.

The phrases "dated 1894" and "dated 1892" cannot be detached from the sentence without making the meaning unclear:

The painting [which one?] is a forgery; the one [which one?] is genuine.

Further examples

Note the distinction and the different punctuation in the following pairs of sentences:

Non-restrictive	Restrictive
William Carlos Williams, the poet, was also a farmer.	The poet William Carlos Williams was also a farmer.
John, who has been drinking, should not drive.	People who have been drinking should not drive.
Many Americans travel to Mexico, where Laetrile is legal and readily available.	Many Americans travel to countries where Laetrile is legal and readily available.
In spring, when the water is high, the lake surges over the rocks.	At times when the water is high the lake surges over the rocks.
The waiters, dressed in their white jackets, are already arranging the chairs on the sidewalk.	The waiters dressed in white jackets serve in the main dining room; those in red serve in the coffee shop.

Self-test and answers

Ready to test what you've learned? Click on the link below:

Test your knowledge

For further information on commas see our page on Coordinating Conjunctions or our grammar and style FAQ. Or take one of the free grammar, style, and punctuation classes offered by the Writing Center.