 It is fairly clear here that Leibniz takes ‘influx’ to refer to the transference of accidents—today we call them tropes or property-instances—as when a guitarist’s fingers give an instance of motion to a struck guitar string. Leibniz holds that it cannot be comprehended how one finite substance could act on another finite substance. For such intersubstantial causation entails the transference or migration of an accident from one substance to another, where a trope passes from one thing to another, which then instantiates it. Such transference is inexplicable; an accident passing (i.e., trope transferring) from one subject to another is impossible (New Essays A vi, 6, 224). Leibniz writes in the Discourse on Metaphysics: