The original political basis of the Shi’a was reinforced from two sources. The first was mystical speculation deriving from the eastern Hellenistic world and supplemented by metaphysical ideas and the doctrine of predestination. This mystical speculation issued in the philosophy of light, which the Shi’a, with the exception of the Zaydiyya, took over. According to this theory, as it developed among them, it was believed that, from the creation of Adam onwards, a divine light (sometimes called nur-i muhammadî) had passed into the substance of one chosen descendant in each generation and was present in ‘Ali and each of the imams among his descendants. By virtue of this divine light, it was believed that secret knowledge (hikma, hikmat) was granted to the imam and immunity from sin conferred upon him. He alone possessed the secret source of knowledge and his decisions alone were decisive and final. It was further believed that man could only acquire knowledge of divine mysteries by being joined to this light through the imams, who, in succession to the prophet, acted as intermediaries between man and God in the search for divine knowledge.