Translation:This bicycle belongs to my brother.
I have the same question as dbaldauf147, wondering why you NEED the pronoun when the indirect object is spelled-out for you in the sentence. If the IO is stated, why is the pronoun necessary?
I should state that I know this lesson is about pronouns, but am curious if it’s correct/incorrect to state the sentence as in my question if you choose not to use a pronoun.
Pertenecer is an intransitive verb, listed "vi" in the dictionary. This means that it cannot have a direct object. "The bicycle belongs to my brother. " is a passive version of "My brother owns a bicycle." Kind of like "The food is pleasing to me." is a passive version of "I like the food." Remember "gustar"? It is not that this is unusual in English to see the preposition "to" and know that it is not the direct object.
When you think about it, you realize that this could be worded "The bicycle is owned by my brother." The true passive voice version ! "The food is liked by me." If you can put a sentence into this form, then you can rest assured that this verb is intransitive and passive (a backwards sentence).
If you put it back into active voice, the passive 'indirect object' or in English the object of the preposition "by" (In this case, English does not call this an indirect object.) becomes the subject and the passive subject becomes the direct object! In Spanish, you just have a list of verbs to memorize that require indirect objects, with "gustar" at the top of the list. http://www.studyspanish.com/lessons/gustar.htm
If a verb is transitive (vt in the dictionary), there will be a direct object or direct object pronoun or maybe one that is understood from the verb. "I write a letter to my sister." "sister" is the indirect object and "letter" is the direct object. You could say "I write to my sister." and you will know that something written is the direct object that "sister" will receive.
I think what is confusing many people is that in Spanish, "a" is used as the personal a in front of direct objects which are people or pets. This looks just like the "a" which means "to", but it is not the same and is not translated into English as it is just a marker that a person or pet is coming next as the direct object. http://spanish.about.com/cs/grammar/a/personal_a.htm
No it isn't a direct object but that isn't obvious. Belongs confuses us I believe so let's replace that with another verb. Hmmm? My brother owns this bicycle. Subject verb and direct object. But we have This bicycle belongs to my brother. So let's assume for a minute we know who they are talking about 'brother' then we can just say "la bicicleta le pertenece'. Remember if we can use 'to him' that it signals an indirect object and then place 'le ' before the verb. Perhaps a grammarian will be kind enough to explain further.
Spanish-speaking people often do omit the indirect object pronoun when the indirect object is a noun, as in your example.
But, grammar-police don't like it.
Here is a further discussion: https://www.duolingo.com/comment/7998752/Are-object-pronouns-necessary The comment by Talca in that discussion is especially helpful