We usually think of extremism in terms of the political ideas one might hold and the willingness to resort to violence for their realization. But simply believing in an ideology on the extreme end of the spectrum, or resorting to violence are not enough to make one an extremist. Extremism is a mindset, a way of seeing the world and others that cuts across ideologies and methods of achieving them, argues Quassim Cassam.

Almost twenty years ago to the day, Mohammed Atta piloted American Airlines flight 11 into the north tower of the World Trade Center in New York. Atta was, by most people’s lights, an extremist. So was Anders Behring Breivik who, ten years later, massacred 69 people at a summer camp in Norway. Wind the clock forward another ten years to 2021, and extremism is still alive and well in Afghanistan and many other places.