"On this arrangement, Sunni doctrine (legal or theological) has always relied on a public discourse

rather than the prerogative of any ecclesiastical authority or the naked assertions of any particular group. In this capacity, theology has always had to validate itself on the basis of some objective, public authority (objective in the sense of everyone having equal access to it). Sunni public authority consisted of two interrelated sources: (1) primary, religious authority, and (2) secondary, interpretive authority. Primary, religious authority, identified as al-naql (or al-manqul or al-sam') is located in the faithful transmission of scripture and its "natural" extensions. Secondary, interpretive authority, referred to as al-'aql (or al-ma'qul) resides in the intellectual/rational interpretation and debate. Beyond their univocal passages and most basic fundamentals, the Qur'an and Sunna are incapable of interpreting themselves or of settling disputes over whose interpretation is correct. This require the intervention of an interpretive authority that lies outside of these texts. Muslim Tradition locates this in al-'aql.

-Sherman A. Jackson, Islam and the Problem of Black Suffering, p. 9-10