Indirect Object Pronouns in Lesson 5.7

I'm trying to get a feel for when to use indirect object pronouns when the IO is mentioned specifically.  The sentence “Jenny le está escribiendo una carta a su padre.” in Lesson 5.7 has both “le” and “su padre.”  The lesson says that you don't need the “le,” but it is very common to use it in this situation.  Does this apply to any sentence with an indirect object whose pronoun would be le or les?  For example, earlier in the lesson there's a sentence “Marta explica su proyecto a Miguel.” which has an IO, but no IO pronoun.  The next example is how you could use the pronoun without the “a Miguel," but I'm wondering if similar to the previous sentence that I referenced another common way to say this sentence might be “Marta le explica su proyecto a Miguel.”  Are there cases where it would be uncommon or grammatically incorrect to add an IO pronoun when the IO is mentioned specifically by name (e.g. a Miguel), or title (e.g. a su padre), or if the IO is a noun that isn't a person?

¡Hola BMW!

Apologies for the late reply!

Your understanding is correct: in any sentence where the indirect object pronoun would be le or les, it is more common for native speakers to include the pronoun in the sentence than it is for them to leave it out. So it would indeed be perfectly possible - and very likely - for a native speaker to say Marta le explica su proyecto a Miguel. 

Generally speaking, “When it doubt, add the indirect object pronoun” can be a good rule of thumb! There are several instances where not including the indirect object pronoun would be grammatically incorrect (for instance, when using verbs like gustar “to like” (e.g. A Manuela le gusta el gato “Manuela likes the cat”), when using a prepositional pronoun (e.g. Te daré el regalo a ti “(I) will give the present to you”), or (most of the time) when placing the indirect object before the verb (e.g. A Juan le cuento todo “(I) tell Juan everything”)). In contrast, including the indirect object pronoun is very rarely incorrect (we'll talk about that more in a moment), and is also typically very common - especially when people are speaking, and especially if the indirect object pronoun in question is le or les. Whether the indirect object is mentioned by name, is a person described as a noun, or is a non-living object described as a noun also doesn't matter - including le or les is still going to be more common than not doing so. 

One rare example of an instance where adding an indirect object pronoun would be incorrect is when the indirect object isn't a pronoun, and you're placing it before the verb to create contrast (e.g. A mi hermana quiero hablar, no a mi hermano “(I) want to talk to my sister, not to my brother”). 

So the vast majority of the time, you can count on adding the indirect object pronoun to be correct!

I hope that this has been helpful!

Saludos,

Liss

Gracias por la respuesta, Liss.  Esa me ayuda.

¡De nada, BMW! :)