fangtray wrote:"The Smiths dislike the Browns because they dislike their children"

In this sentence, they and their can refer ambiguously, but grammatically, They refers to the Smiths because both are subjects, and Their refers to the Browns because they are objects of the sentence. If they are parallel, does it mean that it is not ambiguous?

According to GMAT, the sentence is wrong,but why because "They" refers to the subject of the previous whole sentence, "The Smiths dislike the Browns". "They" can't refer to the Browns, because that would be gramatically incorrect. The Browns is the object, They is the subject.

Yes, when you have two possible noun referents, you prefer the one that has the same grammatical function each time, so "they" should logically refer to the Smiths. After that, any subsequent use of "they" should refer to the same antecedent, and grammatically we would expect that any derivatives of "they," such as "their," refer as well to the Smiths.

The problem is this. How could the Smiths' dislike for their own children logically serve as a pretext to dislike the Browns? That seems extremely strange. If the meaning is illogical or bizarre, the sentence is wrong. Bad sentences are bad not only if they use an incorrect syntax, but also if they end up saying something that we don't want.

Grammatically, then, we would expect "their" to refer to the Smiths, but semantically, we want it to refer to the Browns. It is from this irreconcilable ambivalence that arises the incorrectness.

Lesson: don't just be looking for compliance with a list of rules and an endless string of matchups with anything and everything. ALWAYS LOOK FOR A LOGICAL MEANING FIRST.