The Imamate makes Shia Islam structurally different: the Imams are held to be divinely designated, sinless, and authoritative interpreters, which locates religious authority in a person rather than in scholarly consensus. Twelver Shia — the large majority — hold that the twelfth Imam went into occultation in 874 and remains alive and hidden, to return as the Mahdi. That absence is doctrinally productive: it is why the scholars (the marja'iyya) act as deputies, and why questions of legitimate government have been argued so intensely.