English Grammar ^^

Defining relative clause singles out a particular thing or person from two or more similar things or people, showing which one we are talking about.

Our house is the one which has new paint.
(The new paint distinguishes our house from all other houses.)

A defining relative clause has been essential to the complete meaning of the sentence, so we haven’t set it off with commas. (No commas)
If you delete the defining relative clause, the meaning of the whole sentence is completely different.

Other examples:
I gave a scarf to the girl who organized my stay.
~ identifies the person who received the scarf (i.e. the one who organized my stay.)

I can’t find the book that I was reading.


Non-defining relative clause is not a clause that ‘doesn’t define’. More specifically, it is clause which doesn’t define in that particular context even though the same words in the same place, if punctuated differently, might do so.

Our house is the last one in the street, which has new paint.
(Incidentally, our house also has new paint.)

A non-defining relative clause adds information to a sentence, but is not an essential part of the complete meaning. The meaning of the sentence would not suffer without the non-defining clause. We don’t use relative pronoun, “that”, in non-defining relative clause.
We separate the non-defining relative clause from the main clause, usually with commas.

Other examples:
Our fridge, which hasn’t worked properly for years, has finally packed in.
Einstein, who failed his university entrance exam, went on to win the Nobel Prize.

How to determine when to use non-define or defining clause:

You have to determine if the relative clause is important to identify the person/thing or just adds extra information.
Our house is the one __________.
Our house is the last one in the street _________.

Sometimes you simply delete the relative clause to see if it is important or not in the sentence.

這裹有簡潔易明的答案：


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

早前我上載了一些錄像在Youtube，解釋一些基本的文法規則，這個錄像正正回答你的問題，希望可以幫到你。

http://www.youtube.com/watch?v=A_IUhEwKcg4

good luck!!

You can tell the difference between defining and non-defining clause from the use of comma.



The function of a defining relative clause is to limit the application of the antecedent; where that is already precise, a defining clause is not wanted. The limitation can be effected in more than one way, according to the nature of the antecedent. As a rule, the antecedent gives us a class to select from, the defining clause enables us to make the selection. Thus in our first example the antecedent leaves us to select from the general class of 'men', the defining clause fixes the particular man (presumably the only man, or the only man that would occur in the connexion) 'who called yesterday'. Sometimes, however, the functions of the two are reversed. When we have an antecedent with a superlative, or other word of exclusive or comprehensive meaning, such as 'all', 'only', 'any', we know already how to make our selection, and only wait for the relative clause to tell us from what class to make it. We know that we are to choose 'the best novel': the relative clause limits us to the works of Trollope. We are to choose 'any man' we like, provided (says our relative clause) that he 'knows three words of Greek'. In either case, the work of definition is done by the exclusion (implied in the relative clause) of persons or things that the antecedent by itself might be taken to include.



Example:

Defining Clause

Andy who dines with us tonight is not the Andy who was at school with you.





Non-defining Clause

Henry, who should know something of the matter, thinks differently.