Restrictive and Nonrestrictive Modifiers
Modifiers can be restrictive or nonrestrictive. A restrictive modifier restricts, or limits, the meaning of the modified element. A nonrestrictive modifier gives supplemental information about the modified element without restricting its meaning.
My friend who lives in Chicago says that the city’s museums are among the best.
In the above sentence, the modifier who lives in Chicago restricts the meaning of friend. Which friend? The one who lives in Chicago.
My dearest friend, who lives in Chicago, says that the city’s museums are among the best.
In the above sentence, the modifying clause, who lives in Chicago, doesn’t restrict the identity of the modified element, dearest friend, but gives more information about the friend—namely, that the friend lives in Chicago. The modifier is nonrestrictive.
You can test to see if a modifier is restrictive or nonrestrictive by temporarily removing it and checking the resulting sentence for sense and meaning. A nonrestrictive modifier can be removed without fundamentally affecting the identity of the element it modifies, because the information it provides is supplemental. In the second sentence above, removing the nonrestrictive modifier results in the sentence My dearest friend says that the city’s museums are among the best. The identity of the modified element, my dearest friend, is not affected. In the first sentence, however, removing the restrictive modifier results in the sentence My friend says that the city’s museums are among the best. We’ve lost information that helps identify which friend is being referred to.
Punctuation with Restriction and Nonrestriction
Use commas around nonrestrictive modifiers. Do not use commas around restrictive modifiers.
The Starry Night, a painting by Vincent Van Gogh, is located in the Museum of Modern Art.
Van Gogh’s painting A Starry Night is located in the Museum of Modern Art.
What happens to the meaning of the second sentence if you put commas around the modifier A Starry Night?
Van Gogh’s painting, A Starry Night, is located in the Museum of Modern Art.
With commas, the modifier becomes nonrestrictive, and the sentence reads as though Van Gogh painted only one painting, which, of course, isn’t true. The point is that punctuation can change restriction to nonrestriction and vice versa and therefore can change the meaning of a sentence.