As an ESL learner I always mess up using prepositions. It’s been especially difficult to understand when to use to or for. Are there any rules about this usage?
My mother tongue is Portuguese. Well, I've got trouble especially when I'm saying things like: I have a letter to/for you. (I never know which one is right). Also when I'm talking about directions it gets confusing. I saw one topic here at ELU that assured the right thing to say is "She's leaving for the USA", but I think (I'm pretty sure) "She's leaving to L.A." has the same sense, so, why do we use different prepositions in the same sense? Well, that's hard but that's what makes English the best language on earth! –
Firstly – samrodriguez - please let me say how wonderfully you are expressing yourself in a language other than your own. While I do know the answer to your question I am finding it difficult to compose a "rule" to describe it to you.
Your example gives "She is leaving (from here) FOR the USA." as compared to "She is going TO the USA."
While (in English) one can "leave FROM - for a location" one cannot "leave TO a location".
The combinations are "Leave from (x) for (y)" and "Go to (y) from (x)" (However, one might leave out the "from (x)" in each case.)
So, the statements may be "She is leaving (from) Portugal for the USA" or "She is going (from Portugal) TO the USA." or "She is going TO the USA (from Portugal)" (The parenthetical statements may be omitted.)
As for the statements "I have a letter (which is) for you" or "I have a letter (which is) addressed to you." - you may leave out the words enclosed in parentheses BUT they are (to be) understood in your statement. Hence, you can say "I have a letter for you." and you can say "I have a letter addressed to you." but you must not say "I have a letter to you." (In that case, you CANNOT leave out the word "addressed".)
In English there is a great deal of room for "understood" and "omitted" statements BUT there are limits - and this is one of those limits where one cannot leave too much to be 'understood' without stating it.
There can't be a simple rule. Have a look at a dictionary, then you will see that a detailed description of these prepositions has between 15 and 20 numbers. The primary concept of "to" is movement directed to a point and analogous models. And "to" is used for the dative and as an infinitive marker. "for" corresponds to Latin pro and answers the question "for whom is sth destined" or "for what is sth used". You have to learn the uses of these two prepositions in the course of time. In a question as "What do you need that knife for?" you can't use "to".