 Lewis’s definition of causation also delivers the result that causation is a transitive relation: whenever c causes d and d causes e, it will also be true that c causes e. The transitivity of causation fits with at least some of our explanatory practices. For example, historians wishing to explain some significant historical event will trace the explanation back through a number of causal links, concluding that the event at the beginning of the causal chain is responsible for the event being explained. As we shall see later, however, some authors have claimed that causation is not in fact transitive.