Good sense is the most fairly distributed commodity in the world, Descartes once quipped, because nobody thinks he needs any more of it than he already has. A neat illustration of the fact that gullibility seems to be a disease of other people was provided by Martin Gardner, a great American debunker of pseudoscience, who died this year. In the second edition of his “Fads and Fallacies in the Name of Science” (1957), Gardner reported that most of the irate letters he received in response to the first edition criticised only one of its 26 chapters and found the rest to be fine. Needless to say, readers disagreed about which chapter was the faulty one. Homeopaths objected to the treatment meted out to themselves, but thought that the exposé of chiropractors was spot on, and vice versa.

No group of believers has more reason to be sure of its own good sense than today’s professional scientists. There is, or should be, no mystery about why it is always more rational to believe in science t