The physical sciences display the world as a hierarchy of regresses, in which epistemological levels, observables and unobservables, are integrated with ontological levels, such as part-whole. Homogeneous regresses preserve generic ontologies, while heterogeneous regresses involve radical ontological transitions. Causal explanations map onto these regresses, transcending reference to causal mechanisms by hypothesizing causal powers. Faraday's physics can be adapted as the basis of a transcendental argument to support the necessity of supposing that the world consists of causal powers. The subject of causal powers attributions can not be the world but the world indissolubly linked to apparatus.