Restrictive Clause:
* Defines or limits the noun it modifies.
* Essential to the sentence's meaning.
* No comma is used.
Example:
* "The book which I borrowed from the library is due tomorrow." (The clause "which I borrowed from the library" is essential to identify the specific book.)
Non-Restrictive Clause:
* Adds extra information about the noun.
* Not essential to the sentence's meaning.
* A comma is used before "which."
Example:
* "The book, which I borrowed from the library, is due tomorrow." (The clause "which I borrowed from the library" provides additional information about the book but doesn't change its meaning.)
In Summary:
* If the clause with "which" is essential to understanding the sentence, no comma is needed.
* If the clause with "which" is additional information, use a comma before "which."