Por and para are very common prepositions and have a lot of different functions and meanings. Unfortunately, they are often confused because they can each be translated as for.
Por
This preposition can be a little bit problematic for a learner because it has many different uses. It can be used to:
Express Gratitude or Apology
Muchas gracias por la entrevista.
Thanks a lot for the interview.
Talk about Multiplication and Division
Dos por dos son cuatro.
Two times two equals four.
Express Velocity, Frequency and Proportion
Antes íbamos como dos veces por semana.
Before we used to go approximately twice per week.
Indicate Location or Movement Meaning “Through,” “Along,” “By” or “In the Area of”
Sus máquinas están por todo el mundo.
His machines are used across the world.
Talk about Exchange, Including Sales
Mi papá por ochocientos dólares se compró ese terrenito.
My dad bought that land for 800 dollars.
Mean “On Behalf of,” or “In Favor of,”
Trabajó por su papá que tenía la ferretería.
She worked for her father that owned the hardware store.
Express a Length of Time, Duration
Yo me quedé con mi suegra por cinco años.
I have been living with my mother in law for five years.
Express an Undetermined, or General Time, Meaning “During”
Tuve que caminar como tres kilómetros por la mañana para llegar allá.
I had to walk for approximately three kilometers during the morning to get there.
Talk about Means of Communication or Transportation
Mi esposa es de Montevideo, entonces seguíamos hablando por teléfono.
My wife is from Montevideo, so we kept talking by phone.
Show the Reason for an Errand (with ir, venir, pasar, mandar, volver, and preguntar)
Paso por ti a las ocho.
I will come by for you at eight o’clock.
Express Cause or Reason
Por el frío no se mantuvo abierta la ventana ese día.
Because of the cold they did not keep the window open that day.
Introduce the Agent in Passive Constructions
El libro fue escrito por Octavio Paz.
The book was written by Octavio Paz.
Por also appears in many idiomatic expressions:
por adelantado in advance
por ahora for now
por allí around there; that way
por amor de Dios for the love of God
por aquí around here; this way
por casualidad by chance
por ciento percent
por cierto certainly, talking of
por completo completely
por dentro inside
por desgracia unfortunately
por ejemplo for example
por eso therefore
por favor please
por fin finally
por lo general generally
por lo visto apparently
por medio de by means of
por lo menos at least
por lo tanto consequently
por mi parte as for me
por ningún lado nowhere
por otra parte on the other hand
palabra por palabra word for word
por primera vez for the first time
por separado separately
por supuesto of course
por suerte fortunately
por todas partes everywhere
por todos lados on all sides
por último finally
Me considero mexicano al cien por ciento.
I consider myself as 100 percent Mexican.
Para
This preposition has many different uses. It can be used to:
Indicate Destination
Estudié mis primeros dos años en el TEC de Monterrey en Chihuahua y luego vine para acá, me transferí para acá.
I studied during my first two years at the TEC of Monterrey, Chihuahua and then I came here, I moved here.
Show the Use or Purpose of a Thing
Había otra escuela que se llamaba C. S. Winn que tenía clases para los estudiantes que no sabían inglés.
There was another school called C. S. Winn that offered classes for students who did not speak English.
Express Purpose, Objective, Aim, or Goal
Caminaba una hora para llegar a la escuela y para regresar, era otra hora.
I used to walk one hour to get to school and to go back, another hour.
Indicate a Recipient
El abuelo mío me daba cada ocho días cinco centavos, para mi hermana y para mí.
My grandfather used to give me five cents every eight days, for my sister and for me.
Express a Deadline or Specific Time
Necesito el vestido para el lunes.
I need the dress by Monday.
Express a Contrast from What is Expected
Para un niño lee muy bien.
For a child, he reads very well.
Meaning Changes
It is very important to learn to use these two prepositions correctly, because if substituting one for the other, the final meaning can be dramatically different. Check the two examples:
Juan compró el regalo para María.
Juan bought the gift for Maria (he bought it to give to her).
Juan compró el regalo por María.
Juan bought the gift for Maria (he bought it because she could not).
Por and para can also be used in questions.
¿Por qué? means Why? (for what reason?)
¿Por qué estudias español?
For what reason do you study Spanish?
Porque es un requisito.
Because it’s required.
¿Para qué? means Why? (for what purpose?)
¿Para qué estudias español?
For what purpose do you study Spanish?
Para ser profesor de español.
In order to become a Spanish teacher.