Defining and non defining clauses

Relative Clause (General Category): A clause starting with who, which, that, whose, or where that adds.

1. Defining/Restrictive Clause: Necessary to identify the noun. No commas.

EXAMPLE: The man who lives next door is nice. (Tells us which man)

 2. Non-Defining/Non-Restrictive Clause: Gives extra information. Uses commas. 

EXAMPLE: My brother, who lives in Gerona, is younger. (We know which brother; the clause is just extra info)