Do you know what an “extremist” is? In the wake of the horrible terror attacks on the offices of Charlie Hebdo in France, Barack Obama is speaking very boldly about the need to win the war against “extremists”, and he has announced plans to host a major global summit on “extremism” next month. And on the surface that sounds great. But precisely how are we supposed to determine whether someone is an “extremist” or not? What criteria should we use?