In the not too distant past, it was common to treat Hume's skeptical doubts regarding the justification of our beliefs in causal connections—understood as necessary connections between objects or events—as having appeared per conceptionem immaculatam in his post-Cartesian mind. Thanks to recent efforts by scholars in early modern philosophy, however, we are now more informed about the roots of Hume's conclusions in Cartesian thought itself, especially the influence of Malebranche and his arguments for occasionalism. And by the research of historians (...) of Medieval philosophy we are reminded that many aspects of seventeenth-century occasionalism, in turn, have their ancestry in Latin and Arabic thought of the Middle Ages. In this paper I offer a small contribution to the overall project of illuminating the precedents in Medieval philosophy for the theses and arguments in Malebranche that so clearly influenced the most important and influential philosophical analysis of causation ever. There is a tradition here, where the goal is to undermine claims to discover real causal relations or powers in nature. I will concentrate on one particular aspect or tool of that tradition: the negative argument that we can never perceive a sufficiently necessary connection between any two natural objects or events. (shrink)