Last time, I explained that because prepositions are pervasive, deceptively simple and arbitrary, most people never get them perfect. The solution, I suggested, is awareness, acceptance and letting go of translation.
With some arrogance, I then promised to take on the daunting task of sorting out the uses of para and por, which, by the way, aren’t always prepositions. After far too much study and consideration, I have come to the unscholarly and regrettable conclusion that there is no good way to explain the different uses of para and por.
Oh, sure, I can give you a long list of categories having to do with purpose, goal, specific destination, implied comparison, opinion, motive, intent, agent, obligation, concern, duty, mode of transportation, velocity, frequency, time duration, cause, effect, etc. These categories will work for you much (but not all) of the time in sorting out which of the two words to use. Then comes the hard part: finding a Spanish speaker patient enough to wait several minutes while you put your sentence together.
Anyway, you can look up these categories in any old grammar book. One will do the job of totally confusing you just about as well as another.
What I find more useful, at least as a start to getting the feel of the two words, is contrastive sentences: that is, sentences that are the same except for their use of por or para.
Observe how the following sentences change their meanings according to the use of para or por. Although I have to translate the sentences in order for you to understand them, try to feel rather than translate the meaning.
Para and por as prepositions:
–Tonio compró un sistema de alarma para sus hijos. (Tonio bought an alarm system for his children [as a gift to them]).
–Tonio compró un sistema de alarma por sus hijos. (Tonio bought an alarm system because of his children [in order to feel they were safe]. Or, Tonio bought an alarm system for his children. [He did the buying as a favor to them.])
–Este bus va para Liberia. (This bus goes to Liberia. [Liberia is its destination.])
–Este bus va por Liberia. (This bus goes by way of [through] Liberia. [It passes through on its way to someplace else.])
–Este poema fue escrito para mí. (This poem was written for me.)
–Este poema fue escrito por mí. (This poem was written by me.)
–Adriana le dio ¢1,000 para el café. (Adriana gave him ¢1,000 for the coffee [so he could go buy it].)
–Adriana le dio ¢1,000 por el café. (Adriana gave him ¢1,000 for the coffee. (She paid him this much.)]
–Pedro es muy débil para su edad. (Pedro is very weak for his age. [He is 16, so he should be strong.])
–Pedro es muy débil por su edad. (Pedro is very weak because of his age. [He is old, and this makes him weak.])
–Hizo la cita para la mañana. (He made the appointment for the morning.)
–Hizo la cita por la mañana. (He made the appointment during the morning.)
Para and por used with verbs:
(Keep in mind that porque consists of por and que.)
–Lo digo para que entiendas. (I say it so that you understand.)
–Lo digo porque entiendes. (I say it because you understand.)
–Para ir a bailar, necesitas ¢10,000. (In order to go dancing, you need ¢10,000.)
–Por ir a bailar, se lastimó el tobillo. (Because of going dancing, he hurt his ankle.)
–Estoy para contar toda la historia. (I am just about to tell the whole story.)
–Estoy por contar toda la historia. (I am in favor of telling the whole story.)
–Esto no me gusta para nada. (I don’t like this at all.)
–Espero que todo eso no fuera por nada. (I hope all this wasn’t in vain.)
Sometimes, you can use one or the other, as you please:
–Te amaré para siempre. Te amaré por siempre. (I’ll love you forever.)
–¿Para qué quieres estudiar el ruso? ¿Por qué quieres estudiar el ruso? (Why do you want to study Russian?)
These contrastive sentences by no means give you the full picture.What they may do, however, is begin to give you a feel for the words.
I wanted to leave you with a list of common expressions using para and por. As it turns out, however, very few exist that use para, whereas too many exist that use por. So I will leave you with one lonely example for para and my personal choices for por.
Estar para (to be about to, to be in the mood for):
–Lo siento. Estoy para salir. (I’m sorry. I am just about to go out.)
–Lo siento. No estoy para bromas hoy. (I’m sorry. I’m not in the mood for jokes today.)
Expressions with por:
–por aquí (this way)
–por allá (that way)
–por avión (airmail)
–por desgracia (unfortunately)
–por Dios (for heaven’s sake)
–por fin (finally)
–por lo menos (at least)
–por favor (please)
–por poco (nearly, almost)
–por supuesto (of course)
–por todas partes (everywhere)
–al por mayor (wholesale)
–al por menor (retail)
–por ejemplo (for example)
–por si acaso (just in case)
–por mi cuenta (as for me)
–por casualidad (by chance)
As you can see, not all of these expressions are consistent with the rules and categories you’ll find in a grammar book. Language, you see, has a curious way of doing that.