In the early modern age, two causal models are clearly identifiable: action at a distance—a typical Renaissance paradigm, widespread among thinkers involved in natural magic and seventeenth-century Neoplatonists—and action by contact, on which both the Aristotelians and the Cartesians agreed. Pierre Gassendi too seems to endorse the motto: ‘Nihil agit in distans nisi prius agit in medium’ [Nothing acts at a distance unless it acts through a medium]. In this essay, it will be shown that a third causal model exists, (...) according to which material bodies are surrounded by ‘atmospheres’ of effluvia or qualities, which spread within a circumscribed ‘sphere of activity’, whose extension is peculiar to each body. In particular, it will be shown: what the third causal model was like, from an ontological point of view, that is, how it centred on the concepts of effluvium and spiritus, or qualitas; what this model was like, from a gnoseological point of view; how it was theorized by... (shrink)