Fake news and alternative facts today challenge the notion of truth. Those spreading them undermine the functioning of democratic states. Arnaud Esquerre questions what is at stake in this new and worrying situation, which concerns as much the evolution of politics, the media as scientific knowledge and even our daily lives. He shows the importance of narratives and the effects of language: it is not because a statement is false that it is not effective. To understand such effectiveness, Esquerre proposes to analyze the structures and functions of these statements. He stands for the ideas, nowadays under threat, of truth and democracy.