Board Thread:Naruto Discussions/@comment-26367861-20161025235033/@comment-26367861-20161028005437

personally i think it has to do with being indras reincarnation or simply the sage transferred the half of his chakra to sasuke by fusing it with his mangekyo and actually giving sasuke his rinnegan chakra, this would explain why sasuke's rinnegan had 6 tomoe and could cast genjutsu and shit while madara couldn't, it fused with his mangekyo.