Professor Seyed Mohammad Ghari S. Fatemi examines the very being of reason within Islamic legal theory. Engaging classical Sunni and Shīʿī perspectives, he asks: Is reason a substance, an accident, or a kind of knowledge? This discussion unpacks how uṣūlī scholars understood the nature, scope, and variability of rational faculties, illuminating how metaphysics, epistemology, and theology converge in defining ʿaql.