I need to understand grammatically why, how and when which

Thank you both for your very helpful explanations!

I have a question though. Can that modify a clause before it? I know that which can modify a clause that comes before it but I was just wondering about that. Can you clarify that part for me? Thanks.

Great explanations!

However, I have seen sometimes that "which" modifies an entire clause in some sentences.

Please explain. Thanks!

@metallicafan
Hi...it would be a great learning experience if can you share those sentences... may be we can ask Bkimball to evauluate same.

I also forgot to mention in my post that there is an exception where which might not refer back to immediatly preceding word. when preposition is used as a part of group of words preceding which , pls see the below mentioned example

If antecedent is a part of the prepositional phrase before "which" , "which" may not directly refer back to words it is attatched with.
e.g.
The picture above fireplace, which was taken last year in mexico, is one of my favourites

here , which refers to the picture taken, in such situations :

1) we must try to rephrase the sentence, if possible to ensure that "which" touches the preceding word.
2)if that is not possible to rephrase sentence then there is no harm in usage of which as mentioned above

the ideal construction with which / that is what has been described in above posts, and almost every time i hve seen the usage of "that and which "as per the rules authenticated by Bkimball.

@Bkimball

usage of "which and that" is the one of the most important points in GMAT, and i hve explained something on the fundamentals of this rule, so i would request you to correct me if i am wrong anywhere in my explanation, so there is no misunderstanding on this rule and my post doesnt misguide anyone because i am not master of verbal , just learning Can you also address two questions along with this

1) how frequently do we see usage of which , where "where" might not refer back to immediate preceding word ? ( in context of GMAT )
2) If you could address any situation where "which" might refer back to entire clause preceding "which"(as mentioned by ( metallicafan in one of the previous posts ) because i am yet to learn this aspect if there are any exceptions

Thanks

I advise to refer to the great articles from e-gmat for your understanding.This is from my personal experience.

https://gmatclub.com/forum/noun-modifiers-can-modify-slightly-far-away-noun-135868.html-see the examples.You can clearly get an idea of usage of 'which'.
https://gmatclub.com/forum/learn-how-that-can-help-you-demystify-a-long-sentence-138358.html-see the examples for usage of 'that'.