Quassim Cassam is a notable analytic philosopher, and his book shows many of the virtues of that tradition. It is beautifully clear, thoroughly researched, rigorous and wide-ranging. Its special virtue is the care with which it distinguishes the conspiracy theories that are its topic from more everyday theories about the existence of conspiracies. Everyday theories can be the ordinary currency of historical thought, for conspiracies are common throughout human affairs. Indeed, Adam Smith famously said that whenever people of the same trade meet together, the conversation ends in a conspiracy against the public, or in some contrivance to raise prices. Cassam gives as a less sweeping example the unquestioned fact that there was a conspiracy to blow up the Houses of Parliament in 1605: the Gunpowder Plot. But the conspiracy theories that are the topic of his book are different. I shall follow Cassam by referring to them with capitals, Conspiracy Theories. …
