 This definition covers cases of deterministic causation in which the chance of the effect with the cause is 1 and the chance of the effect without the cause is 0. But it also allows for cases of irreducible probabilistic causation where these chances can take non-extreme values, as in the Geiger-counter-with-dial example above. It is similar to the central notion of probabilistic relevance used in probabilistic theories of type-causation, except that it employs chancy counterfactuals rather than conditional probabilities. (See the discussion in Lewis 1986c for the advantages of the counterfactual approach over the probabilistic one. Also see the entry  probabilistic causation.)