POR

Rule: to express gratitude or apology
Model: Gracias por la ayuda.
(Thanks for the help.)

Rule: for multiplication and division
Model: Dos por dos son cuatro.
(Two times two equals four.)

Rule: for velocity, frequency and proportion
Model: Voy al restaurante cinco veces por semana.
(I go to the restaurant five times per week.)

Rule: meaning "through," "along," "by" or "in the area of"
Model: Andamos por el parque.
(We walk through the park.)

Rule: when talking about exchange, including sales
Model: Él me dio diez dólares por el libro.
(He gave me ten dollars for the book.)

Rule: to mean "on behalf of," or "in favor of,"
Model: No voté por nadie.
(I didn't vote for anyone.)

Rule: to express a length of time
Model: Yo estudié por dos horas.
(I studied for two hours.)

Rule: to express an undetermined, or general time, meaning "during"
Model: Se puede ver las estrellas por la noche.
(One can see the stars during the night.)

Rule: for means of communication or transportation
Model: Prefiero viajar por tren y hablar por teléfono.
(I prefer to travel by train and speak by phone.)

Rule: in cases of mistaken identity, or meaning "to be seen as"
Model: Me tienen por loco.
(They take me for crazy.)

Rule: to show the reason for an errand (with ir, venir, pasar, mandar, volver, and preguntar)
Model: Paso por ti a las ocho.
(I'll come by for you at eight o'clock.)

Rule: when followed by an infinitive, to express an action that remains to be completed, use por + infinitive
Model: La cena está por cocinar.
(Dinner has yet to be cooked.)

Rule: to express cause or reason
Model: El hombre murió por falta de agua.
The man died for lack of water.

Rule: "estar por" means to be in the mood, or inclined to do something
Model: Estoy por tomar café.
(I'm in the mood for drinking coffee.)

Rule: in passive constructions
Model: El libro fue escrito por Octavio Paz.
(The book was written by Octavio Paz.)
por adelantadopor adelantado
in advance