When we’re faced with a choice between Door #1, Door #2, and Door #3, how do we infer correctly that there’s an equal chance of the prize being behind any of the doors? How is it that we are generally correct to choose the shorter of two checkout lines in the supermarket when we’re in a hurry? In his new book, Tychomancy: Inferring Probability from Causal Structure (Harvard University Press, 2013), Michael Strevens – professor of philosophy at New York University, argues that we are all equipped with a reliable, probable innate, and not fully conscious skill at probabilistic reasoning—a “physical intuition” that enables us to infer physical probabilities from perceived symmetries. This skill is found in six-month-old infants watching as red and white balls are removed in different proportions from an urn. But it also underlies important advances in the sciences, such as James Clerk Maxwell’s reasoning when he hit upon the correct distribution of velocities of a moving particle in a gas. In this intriguing essay on a very special type of cognitive capacity, Strevens’ defends controversial claims about the rules guiding our reasoning about physical probability, its probable innateness, and its role in science as well as in everyday judgment.