Zaydism’s emphasis on the philosophy of free will and rationalism rather than on textual literalism is related to the similarities of its theo logical foundations with those of the Mutazili school of speculative theology, which flourished during the eighth through tenth centuries in Basra and Baghdad.13 Zaydism adopted both the principal tenets of Mutazilism and the Shi‘i belief in an imamate vested in descendants of the Prophet Muhammad. Zaydism differs from Twelver Shi‘ism regarding those who are qualified to rule as imam and the nature of his imamate. Unlike the Twelvers, the Zaydi religious heritage maintains that the imam needs not be an infallible and sinless man (ma’sum) with supernatural powers, but should be a learned scholar who is required to lead armed uprisings against tyrants.