This is easiest to introduce with a tragic case. British high command during the First World War frequently understood trench warfare using concepts and strategies from the cavalry battles of their youth. As one of Field Marshal Douglas Haig’s subordinates later remarked, they thought of the trenches as ‘mobile operations at the halt’: ie, as fluid battle lines with the simple caveat that nothing in fact budged for years. Unsurprisingly, this did not serve them well in formulating a strategy: they were hampered, beyond the shortage of material resources, by a kind of ‘conceptual obsolescence’, a failure to update their cognitive tools to fit the task in hand.

Stupidity will often arise in cases like this, when an outdated conceptual framework is forced into service, mangling the user’s grip on some new phenomenon. It is important to distinguish this from mere error. We make mistakes for all kinds of reasons. Stupidity is rather one specific and stubborn cause of error. Historically, philosophers have worried a great deal about the irrationality of not taking the available means to my goals: Tom wants to get fit, yet his running shoes are quietly gathering dust. The stock solution to Tom’s quandary is simple willpower. Stupidity is very different from this. It is rather a lack of the necessary means, a lack of the necessary intellectual equipment. Combatting it will typically require not brute willpower but the construction of a new way of seeing our self and our world.