Post-truth politics poses a specific problem for critical theories. The problem is that the relativisation of facts – the claim that knowledge is merely a product of power, history, and perspective – is a core aspect of present-day ideological thinking. Critical theories have been unable to respond to this challenge, because their critique has been directed against the opposite claim, namely the naturalisation of facts. While acknowledging this problem, this article argues that post-truth discourse actually combines relativisation and naturalisation. It does not simply relativise truth, but also naturalises the belief in specific ‘facts’ – notably the belief that ‘conspiracies are behind it all’. Once we recognise the twin character of post-truth, we must reject the view of Bruno Latour and others who have made critique responsible for the crisis. Instead, it then becomes apparent that there are deep and disconcerting similarities between post-truth politics and the totalitarian and authoritarian ideologies of the twentieth century. The task of critique is to confront and counter this resurgent ideology, thereby providing direction and orientation in the struggle for emancipation.