Soon after the publication of David Lewis’s On the Plurality of Worlds it received reviews in many journals by leading philosophers. In this letter Lewis replies to Philip P. Hanson’s 1986 review from Philosophy in Review, vol. 6, pp. 498-500. Lewis reacts to the charge that he is committed to some kind of primitive modality, despite his claim that he has provided a fully reductive account of the modal in terms of the non-modal. He also provides an interesting insight into how we should understand the debate concerning haecceitism. (© Estate of David K. Lewis.)