on relative pronouns ( in which)

[lisa***]

good day!

i tried hard to find an article explaining the use of prepositions plus relative pronouns , but couldn't find what i wanted. i wonder why there is a need for us to use prepositions before whom, which and so on..

i also want to know the use of " in which " in a realtive clause.
i understand that we use it for things and facts.
in the sentence...

It was the stream in which the elephant and the mouse preferred to swim.

does it make a difference if i omit the preposition " in" ?

where can i find possibly find more articles on prepositions plus relative pronouns.

thank you in advance!

[ppippi]

my guess is that the 'in' is necessary as in the following:

the elephant and the mouse preferred to swim 'in' that stream.

you could probably rephrase the sentence into:

It was the stream which the elephant and the mouse preferred to swim in.

However though, some people think it's wrong to end a sentence with a preposition, and hence the switch?

Juz a guess, ppippi

[Tdol]

With 'which' you need the preposition. If you want to rewrite the sentence without it, use 'a stream where...'.