  Aristotle already by the introduction of a matching pair of active and passive potentialities for each causal interaction comes very close to admitting a separate potentiality for each and every change, something uncomfortably close to the vis dormitiva, ridiculed by Molière, according to which a sleeping pill  allegedly induces sleep just in virtue of its power to induce sleep.   Aristotle, however, subscribes to an even stronger principle, that  causes in effecting change transmit the form they possess to the  entity they effect change in. According to this claim the active capacity of the item effecting change is at its root an actuality, which is synonymous (in the Aristotelian sense) with the effect that is brought about by it. In Aristotle’s favourite example, only a human in actuality produces a human from what is a human in potentiality.  If this is so, a sleeping pill need not only possess an active potentiality for inducing sleep: it needs also to be slumbering  itself.[22]  The principle—which we could term the principle of  causational synonymy—comes from Plato (see e.g. Phaedo 100B–101D), but Aristotle has his own reasons for endorsing it. His science attests to the presence and operation of causally active forms at each level of analysis of the physical  world.[23]   Hence, as we shall see, Aristotle’s forms  are the causally significant components of the substance effecting a  change. Accordingly, when it comes to specifying the moving cause of  an artefact, Aristotle will refer to the art of the craftsman as the fundamental component operative in the change.  In cases where a living being is generated, it is the parental form which is transmitted to the newly emerging living  being.[24] 