Relative clauses in English Grammar

using a relative clause

Defining relative clauses tell us which person or thing we are talking about.
Non-defining clauses give extra unnecessary, but interesting, information about the person or thing we are talking about.

Non-defining clauses give more information without starting a new sentence.
  1. This is a man. I went to school with him. (2 sentences)
  2. This is the man, who I went to school with. (1 sentence using a non-defining relative clause)

Relative Clause Table

Defining

Subject clause Relative Clause
Those people who came late yesterday.
The man (who is) called John.
A place where we won't be disturbed.
Everything (that) I know
The dog that bit my leg

Non-Defining

Subject clause Relative Clause
My teacher ,who also taught my sister, ...
This palace ,where the Queen once lived, ....
This book ,which won a Nobel prize, ...

Restrictive and non-restrictive

Apparently, he lost all his money gambling, WHICH really annoyed his wife.

In this sentence the relative clause is nonrestrictive, ie. is a parenthetic comment which ususally describes, but does not further define the antecedent which is a whole clause as a rule and not part of the sentence. The wife is annoyed because her husband had lost money, and not because of the gambling. Another example of a nonrestrivtive usage is

Reducing relative clauses from participle phrases to infinitive phrases

  1. Students who study at this school must be good at English. ----> Students studying at this school must be good at English. (reduced relative clause using p.phrase)
  2. She's the only scientist who has won 3 awards. -----> She's the only scientist to have won 3 awards. (reduced relative clause using to-inf)