 The first explicit definition of causation in terms of counterfactuals was, surprisingly enough, given by Hume, when he wrote: “We may define a cause to be an object followed by another, and where all the objects, similar to the first, are followed by objects similar to the second. Or, in other words, where, if the first object had not been, the second never had existed” (1748, Section VII). It is difficult to understand how Hume could have confused the first, regularity definition with the second, very different counterfactual definition (though see Buckle 2004: 212–13 for a brief discussion).