The early Mu‘tazilite theologian Abū Isḥāq Ibrāhīm al-Naẓẓām (ca. 760–ca. 845 ce) is usually neglected in histories of Islamic philosophy. This is a pity, for although he was later widely dismissed as a heretic, his thought is important in several ways. While he was a theologian rather than a philosopher, he, like other representatives of the early Kalām, had a fully developed ontology, physics, and epistemology, which are interesting both in their own right and because such early Islamic philosophers as the members of the circle of al-Kindī were, at least to some extent, reacting to the debates within the Mu‘tazila between Naẓẓām, his uncle Abū l-Huḏayl, and their predecessors and contemporaries. Here I will restrict myself to examining a few aspects of Naẓẓām’s thought on ontology and physics, in order to see whether we can extract from the fragmentary remains of his writings some principles that might be said to characterize what I would like to call his scientific epistemology.