Causation and the Semantics of Counterfactuals Haitao Cai Abstract: Semantics of counterfactuals is normally developed according to the principle of similarity, and the key point is to specify the notion of relative similarity. It can be seen in specific examples that causation plays a crucial role in determining the independence of particular facts and thus also in the measure of relative similarity. Counterfactual account of causation is briefly reviewed. Some counterexamples are provided to illuminate its inherent difficulty, which justifies the proposal that causation underlies the semantics of counterfactuals rather than the converse. Event calculus is introduced in order to facilitate discussions on causation and the semantics of counterfactuals. Two notions of causation are defined formally under the framework of event calculus by making use of timing. Given the mechanism of identification of causation, the semantics of counterfactuals is defined in terms of relative similarity. It's argued that the examples about duchess that are used to support the proposal of epistemic reading actually don't work. The example about Kennedy is also analyzed without appealing to epistemic reading.