Impetus

Abstract

Chapter 4 analyzes Fabri’s definition of impetus: “a quality exacting (i.e. compelling) motion, or flow of place, of its subject; or [the quality] which is the proximate cause of the motion of that mobile in which it is, i.e. in that way in which it can be a cause of motion”. In order to fully understand this definition, this chapter begins by explaining Fabri’s theory of qualities. It then delineates the special causal relation between impetus and motion: motion, not being a full-fledged ens, is not produced (producitur) by impetus, but only exacted (exigitur) by it; consequently, impetus is a formal, rather than efficient, cause of motion, while motion is a “formal effect” (i.e. end goal) of impetus. Fabri’s insistence on formal causality (contrary to efficient causality) allows him to adopt a relatively advanced philosophy of motion – to be further discussed especially in Part III.