What is ideology? The answer is simple, if you do not think about it very hard. Ideology is politics in excess – distorted, immoderate and delusional. It is pundits shouting at each other and unruly mobs chanting in the streets. It is an uncle ranting about socialism at holiday dinners or a co-worker lowering his voice to whisper about the dangers of “the system”. Facts are of no avail when dealing with the victims of ideology; rational arguments slide off their brains like rain running down a granite dome.

As part of this, it has also become an unspoken rule to avoid describing your own politics as ideological. Respectable political ideas are best labelled a “belief system”, “theory”, “philosophy”, or even plain old “common sense”. This is because your own politics are obviously reasonable and good, while those of an adversary are demonstrably irrational and false. If you are progressive, “ideology” is what coerces millions of people into conformity with inherited hierarchies and strips individuals of their freedom and well-being. If you are a conservative, “ideology” is a systematic attempt to replace the traditional moral order with faddish and radical ideas that eventually lead to societal decline and collapse. For both sides, escaping ideology is as simple as switching teams and adopting the one-andonly true and defensible politics.

The result of all this confusion and mutual accusation – as the American anthropologist Clifford Geertz brilliantly summed up – is “the term ‘ideology’ has itself become thoroughly ideologized”.Ideology is a snake swallowing its own tail; it is an idea that consumes itself. Indeed, what many people think of as the obvious definition of ideology is nothing more than one more flower growing inside their ideological garden. Every time we seek to rein in ideology, we end up expanding its scope.

But why are we all so confident that our own convictions are immune to the very ideology plainly afflicting everyone else? This book begins from the deceptively straightforward claim that part of our problem is we have forgotten that politics is cultural.