When do you use 'para' and when do you use 'por?

When saying you bought something for someone do you use por or para?

• Answer:

  para. Por ejemplo: Esta carta es para ti. (This letter is for you) For a little longer discussion, you would normally use "para", because most of the time you would buy things to transfer to another person, as in a gift or useful item. If, however, you go to buy something in another person's place, you would use "por". For example, "Her boss sent her to buy paper, but I bought it for her." "Su jefe le mandó para comprar papel, pero yo lo compro por ella."