College Composition / Unit 7 CMP 0167 worked example, 60 to 90 seconds
Deciding Essential or Nonessential
The idea
Deciding whether information is essential is a test you can run on any clause or phrase.
In practice
Work in order. First, find the clause or phrase in question, often one beginning with who, which or that, or a phrase renaming a noun. Second, remove it and read the sentence. Third, ask whether the meaning is unchanged; if it is, the information is nonessential, so set it off with commas and use which for a clause. Fourth, if removing it makes the meaning too general or changes it, the information is essential, so use no commas and use that for a clause. Fifth, check that a nonessential element has a comma at both ends. For example, removing "who teach auto mechanics" from "Faculty who teach auto mechanics requested equipment" changes who made the request, so it is essential.
Where people slip
The test depends on context. "My brother who lives in Denver" is essential if you have several brothers and nonessential if you have one; read the surrounding sentences before deciding.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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