The second person pronouns in Spanish have exhibited numerous variants along its history, not only regarding its stressed forms, but also the agreement that emerges in the inflecting elements that anchor these stressed pronouns. Despite the quantity of studies carried out about voseo, tuteo and ustedeo, none of them has argued what grammatical reasons underlie for so much variation, since they have focused on pragmatic and sociolinguistic patterns without going any further than a mere description. In this article, I aim to account for the linguistic features that have triggered all variants and person disagreements, for every case has undergone the same grammatical process.