Muslims have traditionally understood knowledge to exist for the sake of moral guidance – of individuals, communities, and societies. Knowledge thus holds the key to human prosperity in this world and eternal salvation in the next. This, however, does not make knowledge a simple phenomenon for Muslims. It is divided into the secular and the religious. Secular knowledge, ethics and sciences as attained by human inquiry and effort and verified by rational and experimental analysis, has constituted an important source of guidance for Muslim life in this world. Of great interest to Muslims through the centuries, its worth has been evaluated in terms of its ability to stand up to human examination, developing in relation to human discovery of the world and its ways. In contrast, religious knowledge, both revealed and prophetic, has a supra-human character to it, putting it above ratiocination and experimentation. Its worth thus stands apart from human analysis of its content, verifiable only by determining its accurate transmission from the source of the religion, generally understood in Islam as twofold: revealed source, the speech of God as the Qur a¯n; and prophetic source – reports (h. adı¯th in the singular) of the sayings, actions, and decisions of the Prophet Muh. ammad, referred to collectively as the sunna. To be sure, religious knowledge was never static, but did develop in response to changing realities; moreover, the importance of religious knowledge in Islam did occasionally lead to treatment of secular knowledge (for example, geography and optics) in terms of its accurate transmission. Still, it was the venture of religion, indeed its foundation, for which the transmission of knowledge became, at least in traditional Islam, paramount concern.