There are very few thinkers who have changed how we see the world, and even fewer who have changed how we think about how we see the world. Mary Douglas was one of the very rare exceptions. Her field was culture, but she was as unlike the stereotypical cultural academic as one could imagine. A devout Catholic whose late husband was head of research at Conservative Central Office, she used the decades after she passed retirement age in an extraordinary flowering of enquiry that provided striking insights in fields as diverse as the study of the Old Testament and the politics of climate change.

She was a rare example of a public intellectual whose theoretical apparatus allowed her to think in original ways about almost any topic – for example, in her ideas on enclaves, the small groups which at their most extreme become terrorist cells. Where others emphasise their strengths, she emphasised their weaknesses: how prone they are to splits and sectarianism, and how hard it is for their founders to impose and enforce rules. To survive, they create around themselves what she called a ‘wall of virtue’ – the sense that they alone uphold justice, while all around them are suspect. Yet the very thing that binds them together encourages individuals to compete to demonstrate their own virtue and the failings of their peers. The only thing that can override this fragility is fear of the outside world – and so sects, whether political or religious, peaceful or violent, feed off the fear and hostility of states and societies, using it to reinforce their own solidarity and their own sense of virtue. The implication is clear, and challenging, for Western governments: in the long term, defeating terrorism depends on ratcheting fear down, not up, and on dismantling the ‘walls of virtue’ rather than attacking them head on with declarations of war.

This example is just one of many from a varied and fertile career that took Douglas from field work in the Congo to nuclear power. She was a ‘genius of lateral thinking’, in the words of another anthropologist, Adam Kuper.