Rules of usage
Anna,
What Milagro02 is looking for are concrete rules and she's right they have to be outlined properly in a post. I knew this question would surface at one point or another because they are difficult grammar concepts not easily mastered and the first step is to have clear cut rules. I think the rules need to be defined and placed in a sticky in separate threads for the following:
1) Por y para (This is a huge grammar topic)
2) Ser y estar (Same as above)
3) ?Qu?? y ?cu?l?
-Time is not on my side right now but these rules indeed would be helpful to beginners.
LDG.