Summary: Explains the subtle differences in meaning between the Spanish prepositions por and para when they are used in similar syntactic situations.
Both para and por may be followed by an infinitive and used to denote the end for which an action is intended, but with the following distinctions:
Voy á Nueva York para ver el puente de Brooklin. I am going to New York to see the Brooklyn Bridge.
Ando por ver si puedo dormir. I walk to see if I can sleep.
Iré á España para aprender el idioma. I will go to Spain to learn the language.
Iré á Washington por hablar al presidente. I will go to Washington and try to talk with the president.
Ofrecen dinero por entrar. They offer money to get in.
Dan dinero para entrar. They give money to get in (they pay an entrance fee).
Estudio por aprender. I study [hard] to learn.
Es preciso estudiar para aprender. It is necessary to study in order to learn.
Trabajo por ganar la vida. I endeavor to earn my living.
Necesito trabajar para ganar la vida. I need to work to earn my living.
After estar, if a person is subject, por indicates inclination, and para immediate futurity; por moreover leaves the carrying-out of the inclination uncertain, para implies that is going to occur:
Estoy por salir. I am inclined to go out.
Estoy para salir. I am on the point of going out.
Estoy por creer que es guasa. I am inclined to think it is a hoax.
Estaba para entrar cuando le llamé. He was about to go in when I called him.
But if a thing be the subject, por denotes that the action is yet to be performed, and para that it is to be immediately performed:
La discusión está por concluir. The discussion is as yet unfinished.
La discusión está para concluir. The discussion is about to come to a close.
Está para llover. It is going to rain.