Nothing propels discussions on expertise like spectacular expert mistakes. From disasters involving space shuttles (Columbia, Challenger) and nuclear power plants (Chernobyl, Three Mile Island, Fukushima, Sellafield, Saint-Laurent and dozens of others) to hundreds of noxious medications allowed to remain on the market for decades, science has frequently given citizens reasons to doubt and fear it. Mistakes have created fertile ground for contesting the scientific consensus and for the growth of suspicion with regard to the motives and competence of scientists. Some scholars blame them for the falling trust in science and hence for the crazy year 2016 which in many countries destroyed the belief that there is no alternative to liberal democracy: Donald Trump's successful presidential campaign, the Brexit referendum, and the successes of right-wing populism in Europe and other parts of the world. ‘I think the people of this country have had enough of experts’ – Michael Gove's words have been paraphrased by politicians from Poland to Brazil to France.

Paradoxically, the decline of public trust in science has coincided with a growing scholarly interest in expertise. Since the 1970s, works devoted to expertise have been written on social epistemology, cognitive science, social psychology and above all on the sociology of scientific knowledge. In political philosophy this interest has taken the form of a debate on the superiority of epistocracy to democracy. It has focused on the moral and political legitimacy of government by ‘knowers’, epistemic and ethical justifications, the political incompetence of laypeople, issues of equality and justice, and the effectiveness of expert government. Interestingly, the said discussions never touched on the definition of expertise. For some reason, none of the authors were tempted to explain what kind of technical knowledge it is that we should expect from alleged experts. Disputes between democrats and epistocrats centred on abstract ‘knowers’, quasi- Platonic philosopher kings, fictional characters endowed with supreme technical knowledge (whatever that is) and a moral motivation to use it for the good of the community. There was no room in these reflections for a nuanced approach to expertise.