Karl Popper is best known for his contributions to the philosophy of science and the history of ideas. Elements of Popper's thought were clearly libertarian or conservative in character. His politics, however, were recognisably social democratic. His ideal of an open society was not a free market utopia, but a political community in which diverse people engaged with one another in constructive dialogue to seek political solutions to common problems. If Popper made important and enduring contributions to the libertarian and conservative traditions, it would be a mistake to uncritically...