On Lewis's account, A > C is (a) vacuously true if and only if there are no worlds where A is true (for example, if A is logically or metaphysically impossible); (b) non-vacuously true if and only if, among the worlds where A is true, some worlds where C is true are closer to the actual world than any world where C is not true; or (c) false otherwise. Although in Lewis's "Counterfactuals" it was unclear what he meant by 'closeness', in later writings, Lewis made it clear that he did "not" intend the metric of 'closeness' to be simply our ordinary notion of overall similarity.