Johnson is after all the most accomplished liar in public life — perhaps the best liar ever to serve as prime minister. Some of this may have been a natural talent — but a lifetime of practice and study has allowed him to uncover new possibilities which go well beyond all the classifications of dishonesty attempted by classical theorists like St Augustine. He has mastered the use of error, omission, exaggeration, diminution, equivocation and flat denial. He has perfected casuistry, circumlocution, false equivalence and false analogy. He is equally adept at the ironic jest, the fib and the grand lie; the weasel word and the half-truth; the hyperbolic lie, the obvious lie, and the bullshit lie — which may inadvertently be true.

Johnson’s explanation for all these things is that he suffers from the classical vice of akrasia. He knows what the right thing to do is but acts against his better judgement through lack of self-control. He is, in Aristotle’s words, like “a city that votes for all the right decrees and has good laws but does not apply them”. But Johnson’s lack of so many of the other virtues listed by Aristotle – temperance, generosity (he is notoriously reluctant to reach for his wallet), realistic ambition, truthfulness or modesty – is startling. It is hard to accept that in every case he agrees on what is good, and intends it, but somehow frustrates himself from achieving it – rather than in fact having quite different beliefs, priorities and intentions.