Early Muslim philosophers, theologians, logicians and experts in jurisprudence understand knowledge as “firm true belief supported by evidence”. They consider conjectures as a kind of ignorance, the domain of certain knowledge confined in necessary truths; and the domain of uncertain knowledge limited to contingent facts. From their definitions and postulates, we can conclude that they took “having appropriate source” as the criterion of knowledge. For this reason, they included the qualifications “firm” and “immutable” in their definition of knowledge in lieu (...) of distinction between the definition and the criterion of knowledge and separation of cognitive characteristic features of beliefs from the non- cognitive ones. Their approach in epistemology is externalistic but it accommodates foundationalism and fallibilism while evading epistemological relativism. In this approach, knowledge is defined as true belief with proper source. Having proper source is a criterion for knowledge which is not explicitly stated but is implied by different qualifications introduced by them. A source of belief is proper iff it bears a causal relation of some sort to the state of affairs the belief depicts. (shrink)