A word, phrase, or clause that provides added (though not essential) information to a sentence but does not limit or restrict the element it modifies. A nonrestrictive element is usually set off with commas. Contrast with restrictive element. See also: Restrictive and Nonrestrictive Adjective Clauses.
Examples and Observations:
- "Samsø, which is roughly the size of Nantucket, sits in whats known as the Kattegat, an arm of the North Sea. The island is bulgy in the south and narrows to a bladelike point in the north, so that on a map it looks a bit like a womans torso and a bit like a meat cleaver."
(Elizabeth Kolbert, "The Island in the Wind," The New Yorker, July 7, 2008) - Not all participial phrases are restrictive. Sometimes the referent of the noun is already identified, so a modifier isn't necessary. In such cases, the purpose of the modifier is simply to comment on or to add information about the noun, not to define it. Such modifiers are called nonrestrictive modifiers:
My mother, sitting by the window, is talking to herself.
In this sentence the noun phrase my mother is already specific; it has only one possible referent. Sitting by the window simply adds a detail of information."
(Martha Kolln, Rhetorical Grammar: Grammatical Choices, Rhetorical Effects, 3rd ed., Allyn and Bacon, 1999) - "Health sciences, computer science, engineering and business--fields that have tended to attract a somewhat greater proportion of moderates and conservatives--have grown in importance and size compared with the more liberal social sciences and humanities, where many of the bitterest fights over curriculum and theory occurred."
(Patricia Cohen, "The 60s Begin to Fade as Liberal Professors Retire," The New York Times, July 4, 2008)

