Le vs. se vs. neither one...

Hola a todos. 
I was studying some phrases tonight from the rocket Spanish grammar book, and have a couple questions. 

1) Are le and se interchangeable? I mean, I know se exists because sometimes it's easier to say than le; in English, we do that with "a" and "an". But, is it okay to use either one in every situation, or must you use the correct one? And if it's the latter, how do you know which one to use? 

2) I came across a couple phrases in which it seemed to me "le" should have been included but wasn't.
- The phrase "I'm going to bring Maria" is translated "Voy a traer a Maria." Why is it not "Le voy a traer a Maria" with "Le" referring to Maria? Isn't she an indirect object in this sentence? 
- Another example is "We are going to see my grandmother" which is translated "Vamos a ver a mi abuela." Why not "Le vamos a ver a mi abuela."?
- Lastly, "I called John on the phone" is translated "Llamé a Juan por teléfono." Again, why does that phrase not include "Le" before the verb "Llamé"? 

Thank you for any help!

 

Hola rlandonsmith,

​1) No they are not interchangeable.  ​You should use the correct one for the situation, just as you should use the correct form of a or ​an.  ​As far as knowing when to use which, there are rules.  When Le is used with La or Lo​, Le ​changes to Se.  ​When a verb is used in reflexive mode, then you always use Se.  When you are using verbs in Gustar form you always use Le.

​2)
a. Maria is the DO and not the IO and so you don't use Le.   ​You could say:
​          Voy a traer a Maria.
          Voy a traerla.
​          La voy a traer.
​but you normally wouldn't use ​La and Maria​ together.

​b. It's the same as above. Voy a verla.   etc.

​c. It's the same as above also, only masculine.  Voy a llamarlo. 

If you are studying Spanish with the idea talking like a Spaniard, the rules are a little different.  What I described here is what you find in almost all of Latin America.

​One example to help with differentiating between DO and IO and to see Le become ​Se:
​I'm going to bring Maria to my grandma.
​Voy a traerle a mi abuela a Maria .
​Le voy a traer a mi abuela a Maria .
​
I'm going to bring her to my grandma.
Voy a traérsela a mi abuela.
​Se la voy a traer a mi abuela.

​

 

Thank you for the response! It was very helpful. 

However, it leads to one more question. In the sentence, "I called John on the phone" we don't say Le in front because John is a DO. However, Rocket Spanish translates a similar sentence, "I'm going to call John tomorrow", as "Le voy a llamar a Juan mañana." Why does this sentence contain "Le"? 

Again, thanks for the help. 

That example is correct in Spain where ​Le ​can be used as a DO when referring to a person.  However, in most of Latin America it's better to use Lo.  ​Both would be understood, but one is grammatically correct in Spain and the other in Latin America.  I'm not expert on the differences between Spanish Spanish and Latin American Spanish, but this is one of the differences as I understand it.

​As to why RS uses this form for the example you gave, I don't know.  They do occasionally throw in a vosotros conjugation also, which is mostly for Spain.  I do know that RS, like other things, is not perfect  but the forum helps with that.  And these types of discussions help to clarify.

Well, this week I began two weeks of formal grammar review here in Peru.  This afternoon I asked my instructor about this.  She confirmed that everything I said here is grammatically correct.  However, she added that it is "accepted" to use Le ​if the DO is a person.  She also stated that this goes for ayudar, bendecir, etc.  Although I don't recall hearing ​llamarle, the other two, ​ayudarle and bendecirle, ​are very common here.  So to review, here's the correct grammar:

Llamo a Juan - Lo llamo.
​Puedes traer a tu hijo. - Puedes traerlo.
​Ayudo a Juan y a Carlos - Los ayudo. 
​Que Dios bendiga a usted - Que Dios lo bendiga.

​Espero que (a usted) le sea una ayuda.