Indirect object use
"Juan le da libros a Maria"
"Juan da lecciones a María". Le is not used.
Both Google and Bing translators agree on this. Can the direct object determine when the indirect objects is used?
2 Answers
"Juan da lecciones a María." is incorrect. In Spanish the Indirect object pronoun and the indirect object itself can be used in the same sentence. Sometime the actual indirect object itself may not be necessary
EX. Le di a Maria una falda bonita. Le di una blusa también. As you can see I didn't have to mention María in the second sentence.
For a fuller explanation on this, here's a link to my article on the subject in case you missed it.
Direct and Indirect Object Pronouns
I have to disagree with Daniela. "Juan da lecciones a María" is unusual but it´s not incorrect. When we say "Juan le da lecciones a María" the part "of María" is simply for clarification and not necessary for grammatical correctness, but even if we don´t need to clarify, this is the most common way to say it just from habit..
The personal pronoun is absolutely necessary, however, when the indirect object precedes the verb. In this case there is just one correct sentence structure: A María, juan le da lecciones.