Dominic Cummings, chief adviser to the Prime Minister, thinks that there is no ‘better book than Thucydides as training for politics’. But what does he ‘teach’? His ‘lessons’ are legion. Herewith some possibilities.

In his history of the war between Athens and Sparta (430-404 bc), in which he briefly participated, smart one-liners leap off the page: ‘Humans are dominated by three motives: honour, fear and advantage’; ‘Identity of interests is the surest bond between states and individuals’; ‘Men consider what is pleasant to be honourable and what is advantageous, just’; and so on.

Typically of a Greek, Thucydides distinguished sharply between thought and action. Describing a ferocious civil war, he reflected that in peacetime it was normal for sound judgment to prevail, but war, being a ‘violent teacher’, brought out the uncontrollable passions in men: those of sound judgment got nowhere. His hero Pericles advised balance: ‘We have the ability to judge or plan rightly in our affairs, because we do not consider thought an obstacle to action; no, the obstacle is rather the failure to think things through first, in order to foresee outcomes, before action has to be taken. We also combine resolve with our calculations about the job in hand; for others, their ignorance produces recklessness, while calculation produces only dithering.’ But Athenians intent on subduing the island of Melos argued: ‘We know that by a law of nature, wherever men have the power to rule, rule they will. This law was not made by us… we inherited it.’

So what drives Mr Cummings’s policy: pure advantage? Instilling fear? Violent action? Calculation + resolve? Sheer brute force? Whatever it is, there are no guarantees. As the Athenian general Nicias said of a dangerous expedition to Sicily in 415 bc: ‘I have committed myself as little as possible to chance and have armaments as fit as can be for the task.’ It ended in total disaster. Thucydides knew ‘how unpredictable war is… The longer it goes on, the more of a gamble it becomes’. Doubtless Mr Cummings has planned for chance too.