Like many men born to scholarly families at the turn of the fifteenth century, ʿAbd Allāh Ibn Ayyūb al-Qādirī moved from Damascus to Cairo as a young adult to pursue a career in law. Though this legal career soon foundered, Ibn Ayyūb gained a reputation in Cairo for perfectly embodying the pietistic and professional ideals of the Islamic learned elite, or ulama. In this article, I introduce this hitherto unstudied figure of the late Mamluk era with reference to his treatise on a major scholarly debate of his day: the extent to which natures, or the elemental composition of celestial bodies, humors, miasmas, etc., acted with causal independence from God, and whether this causal independence accounted for the incidence, spread, and cure of contagious disease. Entitled “Blocking the Means of Harm Caused by Teaching the Causal Efficacy of Natures,” Ibn Ayyūb’s treatise on this natural philosophical controversy is didactic and homiletic. He states at its outset that he composed it in order to acquaint inexperienced ulama with the concept of natural causal efficacy and demonstrate the speciousness of arguments made in its favor. Rather than constitute an original treatment of this subject, I argue that “Blocking the Means” served as an occasion for Ibn Ayyūb to project his adherence to the robust intellectual standards of his fellow ulama. By the fifteenth century, this class of scholars had tasked itself with protecting Islamic scholarly discourse from compelling yet nevertheless fallacious forms of knowledge. This mission included interrogating the demonstrative status of medicine and astrology—disciplines whose legitimacy the ulama purportedly questioned amid outbreaks of epidemic disease in the late Mamluk period. Accompanied by a biography of Ibn Ayyūb drawn from contemporary sources, the following analysis of “Blocking the Means” will provide further sociocultural context for natural philosophical debates in fifteenth-century Egypt, as well as document how the ulama of this era understood the implications these debates held for their professional and pietistic identities.