Hi there, I have been studying English as a second language for quite some time now but I still get confused when it comes to using prepositions.

Please look at the following sentences and tell me the difference b/w them:

Her obsession with mirrors is unfathomable
Her obsession to mirrors is unfathomable.

Are both of those sentences correct? Or do they both portray a different visual image?

How about these two sentences:

The same thing happened with me on my first day at school.
The same thing happened to me on my first day at school.

Can to and with be used interchangeably?

Appreciate your time and help.
For the first pair of sentences, "with" is correct.

For the second pair of sentences, "to" is correct. But, I have heard some people use "with" in informal language.

I guess the explanation can be that "obsession with mirrors" shows a relationship that the mirrors are the object of the obsession. Also, "thing happened to me" means that the "thing" affected "me", and the "thing" is a circumstance. I'm still unsure about the specific grammatical reasons, but the difference could come from the fact that obsession is a noun and happened is a verb.
Thanks, your logic makes sense.

Oh and I made the thread before i had made my account, hence it says 'post by anonymous' : )
Students: Are you brave enough to let our tutors analyse your pronunciation?
there's generally no rules behind prepositions. They're (generally) just patterns you have to learn. just like irregular verbs. Obsessed-with, fascinated-by, happened-to, etc.