As a beginner, it is probably best to learn the two prepositions separately and to think of por as a preposition that usually indicates cause or motive, rather than simply as a translation for "for." (It also often means "by," but it isn't the only Spanish preposition translated that way.) So in the examples of por usage that are given below, a translation (sometimes awkward) using a word or phrase other than "for" is given, in addition to a translation using "for" (where appropriate). By learning how por is used rather than how it is usually translated, you will find it easier to learn in the long run.
Here, then, are the most common uses of por:
To indicate the cause of or reason for something: In such usages, por can often be translated as "because of."
- Examples: ¿Por qué? (Why? Because of what? For what?) Trabajo aquí por el dinero. (I work here because of the money. I work here for the money.) No podemos salir por la lluvia. (We cannot leave because of the rain. We cannot leave due to the rain.) Conseguí el empleo por mi padre. (I got the job because of my father. I got the job through my father.)
To indicate support for or action on behalf of some person or cause:
- Examples: Voto por Julia González. (I am voting for Julia Gonzales. I am voting in support of Julia Gonzalez.) Es socio de Médicos Por Justicia. (He is a member of Doctors for Justice. He is a member of Doctors Supporting Justice.) Mi padre está por no violencia. (My father is for nonviolence. My father is a supporter of nonviolence.) Es el representante por el estado de Nueva York. (He's the representative for the state of New York. He's the representative on behalf of the state of New York.)
To indicate an exchange of some sort: One common use of this type is indicating how much something cost.
- Examples: Compré el coche por $10.000 dólares.(I bought the car for $10,000. I bought the car in exchange for $10,000.) Gracias por la comida. (Thanks for the meal.) Quisiera cambiar la camisa por una nueva. (I'd like to exchange the shirt for a new one.)
To indicate being in a place: In such uses, por doesn't indicate a destination, but rather proximity or placement. It is often translated as "by" or "through."
- Examples: Pasaremos por San Francisco. (We will pass through San Francisco.) La escuela no está por aquí. (The school isn't near here.)
As a translation for "per": In informal contexts, a translation of "for" rather than "per" is common in English.
- Examples: El tres por ciento tiene dos coches. (Three percent have two cars.) Compré dos regalos por persona. (I bought two gifts per person. I bought two gifts for each person.) Trabajo 40 horas por semana. (I work 40 hours per week. I work 40 hours a week.)
To mean "by" when it points to someone performing an action: Common uses are indicating the author of a book or other work, or indicating the performer of a passive verb.
- Examples: Fue escrito por William Shakespeare. (It was written by William Shakespeare.) Los tacos fueron comidos por los estudiantes. (The tacos were eaten by the students.) Prefiero el libro por Isaac Asimov. (I prefer the book by Isaac Asimov.) Puedo estudiar por sí mismo. (I can read all by myself.)
In certain set phrases: Such phrases are commonly used as adverbs. The meaning of such phrases isn't always obvious by translating the words individually.
- Examples: por cierto (by the way), por lo general (generally), por supuesto (of course), por otra parte (on the other hand), por fin (finally), por lo menos (at least)