This chapter takes off from Max Weber’s famous lectures on politics and science as ‘vocations’ to explore the concept of ‘modal power’, that is, the power to determine what is possible. Politics and science are complementarily concerned with modal power, in ways that go to the heart of Michael Dummett’s influential metaphysical characterisation of the antirealism/realism distinction, which the chapter pursues across several philosophical fields, including logic, epistemology, jurisprudence and finally historiography. The chapter adopts a ‘post-truth’ perspective in the sense that modal power is treated from an ‘antirealist’ standpoint, in which ‘the name of the game’ is to expand one’s own sphere of possible action while constraining that of the opponent. That world of constrained possibilities is the ‘actual’ world, whose relationship to other possible worlds fluctuates over time in ways that resemble quantum effects but are most clearly captured by ‘revisionist’ historiography. The chapter ends with a discussion of the contrasting attitudes to such historiography in politics and science.