n 18 March, Boris Johnson told parliament he was “absolutely certain” that the government’s Covid-19 strategy would “succeed”. This is the kind of vacuous jabbering that has led critics to complain of his “bluster”. But what is that exactly? Probably from the old Norse for a gale, “bluster” has long meant a violent wind, or figuratively a stormy passion. Since speech is also a kind of wind, “bluster” has also been applied to a manner of speaking. The OED defines it as “boisterous inflated talk, violent or angry self-assertion, noisy and empty menace, swaggering”, many of which might reasonably be applied to the prime minister. The modern use of “bluster” to mean a kind of smokescreen of fact-agnostic verbiage, however, might be more influenced by the similar-sounding “bluffer”. (The etymology of that is uncertain, though a “bluff” was once a blinker for a horse.) As political criticism, “bluster” might be unhelpful in conflating different things: windy rhetoric, shameless ignorance or actual lying. Arguably Johnson’s speech is a much better exemplar of what the philosopher Quassim Cassam calls “epistemic insouciance”: the state of simply not caring what the facts are. In other words, it’s not bluster; it’s bullshit. • Steven Poole’s A Word for Every Day of the Year is published by Quercus.