Using En vez de instead of por?

Question

I’m assuming en vez de can’t be used in the same way as por because there is a sense of obligation on behalf of the subject when using por? Yo tomé el carro en vez del autobús. Using por here would be wrong. Yo hice el trabajo por él porque estaba enfermo. En vez de here, would be wrong, right?

Silvia Píriz · Accepted Answer

Hola Devin P.
Exactly, these two structures express different ideas, so they are not interchangeable.
En vez de means “instead of” or “rather than”, so it is used when you are replacing one option with another:
Tomé el carro en vez del autobús. = “I took the car instead of the bus.”
On the other hand, por in sentences like Hice el trabajo por él means “on behalf of”, “for someone”, or “in someone’s place”. It often implies doing something for another person, sometimes because they cannot do it themselves:
Hice el trabajo por él porque estaba enfermo. = “I did the work for him because he was sick.”
Using en vez de here would sound wrong because you are not replacing him with another option; you are acting on his behalf.
¡Hasta pronto!
Silvia