How do you define extremism? That depends on whether you want a definition with which most people can agree, or one that is meaningful. A definition acceptable to most people must necessarily be broad and bland. One that has more meaning will inevitably be controversial and contested. And therein lies one of Michael Gove’s problems in his new definition of extremism. Such a definition is either unnecessary or it creates the very problems it is supposed to solve. There are certain issues that most people would accept are extreme: the advocacy of Nazism, for example, or a demand for the...