 (iii) Asymmetry. If A causes B, then, typically, B will not also cause A. Smoking causes lung cancer, but lung cancer does not cause one to smoke. One way of enforcing the asymmetry of causation is to stipulate that causes precede their effects in time. But it would be nice if a theory of causation could provide some explanation of the directionality of causation, rather than merely stipulate it. Some proponents of probabilistic theories of causation have attempted to use the resources of probability theory to articulate a substantive account of the asymmetry of causation.