“Post-truth” was coined in 1992 to describe the Iran-Contra scandal and the Gulf War but the popularity of the expression has rocketed more recently, leading to its being chosen by Oxford Dictionaries as the 2016 “word of the year”. The prefix “post”, Oxford explains, means “belonging to a time in which the specified concept has become unimportant or irrelevant”. And yet everywhere the intelligentsia and the tech industry are loudly worrying about truth and how to save it. It’s as if truth, far from having become irrelevant, has shot to the top of the cultural agenda.