Review ofTychomancy- Michael Strevens,Tychomancy: Inferring Probability from Causal Structure. Cambridge, MA: Harvard University Press (2013), 280 pp., $39.95 (cloth).

Abstract

Another example Strevens discusses in some detail is Maxwell’s 1859 discovery of the Maxwell-Boltzmann law, according to which the velocity of gas molecules in equilibrium has a Gaussian probability distribution in each direction. As Strevens points out, Maxwell’s original derivation of the distribution, from apparently a priori symmetry assumptions, is not only unsatisfactory, but doesn’t even do justice to Maxwell’s own evidence. Maxwell knew the probabilities, but he didn’t know how he knew. Tychomancy is a welcome philosophical contribution to an important topic. Probabilistic judgements are central to our scientific and everyday understanding of the world, but we know little about how these judgements are formed and what makes them reliable. Strevens addresses these questions in a pleasantly accessible but careful style, combining insights from child psychology, the history of science, and the mathematics of probability. So what guides our probabilistic judgements? From examples like dice one might think they are directly based on physical symmetries, following some principle of indierence. But things are not that simple. We know that a die tossing machine is unlikely to produce the usual probabilistic patterns, despite the physical symmetries of the die. We also realize that if a die is rolled without shaking, then some outcomes are at a disadvantage. Moreover, it is not obvious how physical symmetries enter into evolutionary explanations,