The Qurʾan is replete with condemnation of uncritical acceptance of inherited doctrines and exhortations to have an unwavering conviction in its veracity. This dual imperative spurred philosopher theologians to explore the nature of belief, distinguishing its commendable from its condemnable forms. Central to these explorations was the question of certain knowledge: its nature, locus, and causes. The definition of knowledge, however, remained elusive. For Akbarian philosopher theologians, this is because of the rationalist manner in which the question is approached. Rationalism in this instance being the the view that knowledge in its highest form is graspable by reason. Akbarians distinguish between the heart (qalb) and reason (ʿaql), making the former the locus of true knowledge. Like their rationalist interlocutors, they take it to be the case that the epistemic and the ontological realms are related. Yet they distinguish themselves by the way in which they establish such a relation. This paper points to the manner in which the relationship between both realms is established, showing how it is rooted in the Akbarian formulation of the relationship between essence and existence (wujūd). It argues that the problems faced by rationalisms arise from their ontology in which essences are fundamental. In an Akbarian ontology where wujūd is fundamental, the essential link between knowledge and existence is established, tying both domains inextricably together and establishing the ontological grounds for certain knowledge. I conclude with reflections on the place of this conception in the history of philosophy and whether it can help open up new possibilities for contemporary thought.