Los libros de Benedetti ya los tenemos - Pronoun help?
Los libros de Benedetti ya los tenemos. Ya tenemos los libros de Benedetti.
Hi so this is one of many many sentences that confuse me, obviously I understand it, and I understand that the "los" is a direct object pronoun, but I don´t know the rules for when I have to use the pronouns like this despite the fact i´ve already mentioned the direct object by name.
Another one:
Hace tiempo que no veo a Marta. - A Marta hace tiempo que no la veo.
If anyone could share with me their understanding of the rules, or a web page that they have found particularly helpful that explains this (not the first one you find when you google it, I can use google! The problem is they always explain silly thigns like the difference between lo and le, which I understand, and they don´t go into enough detail after that) I´d be really happy, thanks!
4 Answers
You first question involves the "redundant" object pronoun. I can tell you the grammar rule that will tell you when to use it, but I can only suppose why it must be used.
Los libros de Benedetti (d.o.) ya los tenemos.
The grammar rule that makes the los necessary in that sentence is that if the d.o. is stated before the verb, then you must have a "redundant" d.o.p. I suppose one reason for requiring the pronoun is to warn you that Los libros de Benedetti is not going to be the subject of the verb, but rather the d.o. of the verb. Sort of like how Spanish uses "anticipatory" punctuation marks.
Ya tenemos los libros de Benedetti.
Notice that the "redundant" d.o.p. is not needed when the d.o. follows the verb in its expected location.
Hace tiempo que no veo a Marta. - A Marta hace tiempo que no la veo.
This is the exact same situation. When the d.o. (Marta) is located before the verb, the "redundant" d.o.p. is required. When it is in its expected position following the verb there is no "redundant" d.o.p. Here the preposition "A" is used similarly to tell you that Marta is going to be an object (d.o. or i.o.) of the verb rather than the subject of the verb. In this sentence Marta is a d.o. and the "a" is the personal "a". In a sentence like A mí me gusta...the preposition "a" tells us that the mí is an i.o. and the "redundant" i.o.p. is used.
As for which article most helped me understand the "redundant" i.o.p. or d.o.p., here it is.
Note: In this article it also states:
However, when the object follows the verb, a redundant pronoun is usually (optional).
While this is true, it varies from the rule that Paralee uses in the lessons concerning the i.o.p. She recommends always using a redundant i.o.p. if there is an i.o. (no matter which side of the verb it is located on.) Since this article says that it is optional and, therefore acceptable to use it, then go with Paralee's recommendation. As Lazarus said in one of his threads you will be correct using it 99.9% of the time. The instances where it is incorrect to use it are very rare.
However, don't use the "redundant" d.o.p. if the d.o. follows the verb. [unless it is a personal pronoun].
When the direct object precedes the verb, you have to include the pronoun before the verb as well.
This is explained here in section 5.2 (you have to click again to get to the final page on pronouns.)
The reason is to avoid possible ambiguity between the direct object and the subject.
Why was your answer so short, and mine so long??
That's probably why my answers are described as "snarky" while yours are described as "this should be a reference article." 
Los libros de Benedetti ya los tenemos.
We can (and in conversation, often do) obtain exactly the same effect. However, we tend to use different punctuation (and intonation). "Benedetti's books? We already have them." The "them" in English is just as necessary as the "los" in Spanish. The first phrase (in Spanish) or the first sentence (in English) confirms/reasserts what one is talking about and the "them" (English) or "los" (Spanish) refers/relates back to the mentioned items.
