John Allen Paulos

Most people nowadays who claim to lack a ‘mathematical brain’ can easily sit down to multiply 231 by 34 or divide 2119 by 138 and come up with the answers. Yet in the 15th century Northern European merchants had to send their mathematically gifted sons to Italy to learn how to accomplish these feats. Arabic numerals were not yet in wide use, and German universities weren’t the place to find out about the arcane arts of multiplication and division. Before smiling indulgently, however, try multiplying the Roman numerals DCL and MLXXXI or dividing MDCCCVII by CCLXIV without first translating them into our own system of numerals. So who has more number smarts, the present-day self-styled innumerate or the mathematically gifted German student from five hundred years ago?‘

Studies have shown repeatedly that children with bigger feet reason better than do those with smaller feet. Many of you have probably noticed this very strong correlation yourselves. Of course, there is no causal connection here. Children with bigger feet reason better because they’re older. Irrationality: The Enemy Within is about the mistakes, misconceptions, and unfounded assumptions that muddle decision-making in everyday life and in a wide variety of occupations. People don’t notice associations that are strong, they believe in causal connections that are non-existent, infer significance where there is only chance, remain immune to overwhelming evidence, and are over-responsive to dramatic incidents. One of the most appealing aspects of this book is that its grand pronouncements are few and its specific illustrations plentiful. The author does not attempt a general analysis of rationality. Hume’s notorious problem of induction, for example, is mentioned only to be dismissed, as are concerns about our ultimate ends or purposes. The book is, rather, a compendium of psychological studies and real-world instances whose central thesis is that most of us make critical mistakes in reasoning.