Which statement best describes essential versus nonessential clauses?

• A. They define the noun they modify and are not set off by commas.
• B. They provide extra information and are set off with commas.
• C. They always begin with who or which.
• D. They are optional in formal writing.

Answer: (B)

Understanding essential versus nonessential clauses means knowing when information is needed to identify the noun and when it’s just extra detail. Essential (restrictive) clauses define exactly which noun we’re talking about and don’t use commas. Nonessential (nonrestrictive) clauses add extra information about the noun and are set off with commas.

For example, essential: The book that has a red cover is mine. Here, the clause helps identify which book. If you remove it, the meaning changes. Nonessential: The book, which has a red cover, is mine. The clause adds extra detail about the book, but the main point (“the book is mine”) still stands without it, and it’s separated by commas.

The correct statement describes nonessential clauses as providing extra information and being set off with commas. The other ideas aren’t accurate: essential clauses don’t use commas because they’re needed to define the noun; essential clauses aren’t restricted to starting with who or which; and these clauses aren’t simply optional in formal writing.