Relative clauses

Non-Defining Relative Clauses

•Add extra information to a sentence:

Apples, which are my favourite fruit, are very good for you.

•If you take away a non-defining relative clause, the sentence still makes sense:

•Apples are very good for you.

NOTICE THAT THIS KIND OF SENTENCE NEEDS COMMAS TO SEPARATE THE CLAUSES.  

Defining Relative Clauses

•Add vital information to a sentence - without this information, it would be difficult to know what is meant:

The woman who lives next door has been arrested. 

•If you took out the clause, the sentence wouldn’t make sense:

The woman has been arrested.  (What woman?!)

NOTICE THAT COMMAS ARE NOT NECESSARY IN THIS TYPE OF SENTENCE.

http://learnenglish.britishcouncil.org/en/grammar-reference/relative-clauses-non-defining-relative-clauses

http://www.englisch-hilfen.de/en/exercises/pronouns/relative_pronouns.htm

http://www.autoenglish.org/generalgrammar/gr.relative.i.htm