Should I use comma before "which", "where", and "who"?

Deciding whether to use a comma before which, where, or who means determining the function of the relative clause. These words are called relative pronouns. When the information that follows the relative pronouns is essential to the sentence, you do not use a comma. When the information is extra and the sentence is clear without it, you put a comma before the relative pronoun.

Example: I want to eat at a restaurant where they serve sushi. (The sentence doesn't make sense without where they serve sushi because it clarifies what type of restaurant it is.)

Example: My dog, who loves to play fetch, is a Scottish terrier. (Who loves to play fetch is not crucial to the sentence. You can take it out, and the sentence still makes sense.)

When the nonessential relative clause is in the middle of the sentence, the comma goes before the relative pronoun and after the clause. When it's at the end of a sentence, only put a comma before the relative pronoun.

Essential Relative Clause Examples

• Are you the person who brought the cake?
• I want to visit a place where there are beautiful beaches.
• I need a book which explains punctuation rules in great detail.

Nonessential Relative Clause Examples

• Her book, which has been in the works for years, releases in October.
• My daughter, who is in college, is nineteen years old.
• I'm traveling to New York, where my best friend lives.
• There was a tornado, which was strange for November.