P1-c Use commas to set off a nonrestrictive word group.
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To test whether a word group is nonrestrictive (supplemental, nondefining, and thus nonessential) or restrictive (defining and thus essential), read the sentence with and without the word group. If the sentence is essentially unchanged in meaning without it, the word group is nonrestrictive. Use commas to set it off.
| NONRESTRICTIVE | The oldest fishermen, grizzly sea salts wrapped in an aura of experience, led the way. |
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Conversely, if omitting the word group changes the meaning of the sentence, it is restrictive. In this case, do not use commas.
| RESTRICTIVE | Body-mapping technologies can give video games a sense of realism that was not previously available. |
Use a comma to set off a nonrestrictive word group at the end of a sentence.
Use a pair of commas to set off a nonrestrictive word group in the middle of a sentence.
(See also P2-b.)