David Lewis is most famous in the analytical metaphysics literature for his analysis of the truth conditions of counterfactual conditionals in terms of possible worlds, and for his analysis of causation in terms of counterfactual conditionals. He uses a notion of comparative similarity of possible worlds in his analysis of counterfactual conditionals. However, since he attributes reality to possible worlds he has attracted many criticisms. The aim of our paper is to present some counterfactuals whose account cannot be given within (...) a Lewisian framework, and to point to some devastating results for Lewis of such an inadequacy. (shrink)