What Protection From Error Licenses as Evidence

What protection from error actually licenses is a change in what counts as evidence. A legal system that treats its jurists as fallible has to weigh a scholar's report against other reports and against the possibility he erred; a system that holds its central authorities incapable of error can instead treat their sayings as directly binding, the way a Quranic verse or a hadith of the Prophet is binding, which is why Twelver jurisprudence developed an entire second corpus, the collected sayings of the twelve Imams, standing beside the Prophet's own hadith as a source of law rather than as commentary on it.

Zaydi doctrine, built around a different model of leadership, never made that move. A Zaydi imam is a qualified descendant of Ali who rises openly, gathers support and rules, a role defined by action and recognized qualification rather than by an inherited, protected status, and Zaydi jurisprudence accordingly treats an imam's individual rulings as subject to correction like any other scholar's. The difference is not a matter of degree, more or less deference to a respected leader, but a difference in what kind of thing an imam's statement is taken to be: a fallible legal opinion in one tradition, a source of law itself in the other.