Doubt is the lifeblood of the academy. Historians and political scientists try never to take on trust any public statement that cannot be independently verified. Scientists look for every possible alternative factor and explanation before claiming that there is a causal link between A and B. Philosophers have even been known not to take their own existence for granted. An attitude of radical scepticism is essential for most serious research.Yet there is also a point at which such scepticism becomes pathological and irresponsible.