For decades, it was fashionable to call the concept of truth – even scientific truth – into question. For those who considered modernity to be completely surpassed, reality was a simulacrum, everything was relative, there was no such thing as objective references but “texts”, and “truth” was nothing but masked oppression. This intellectual trend, despite facing some resistance and ultimately being ridiculed by the Sokal Affair, is alarming. It coincides with the rise of the term “post-truth”, which was proclaimed “Word of the Year” by Oxford Dictionaries in 2016. In a world living in peace with relativism, or at most with “liquid” and “weak” truths, the preoccupation with truth is back. What was long considered a topic for philosophers or theologians is now reaching newspapers’ op-eds and the political and legislative agenda. Everyone in a position of power and influence seems concerned by the dissemination of so-called “fake news” and illiberal extremism. But this strong revival of populism and irrationality is provoking a reaction. There is much talk nowadays about fact-checking, Big Data, or mechanisms …