Louis Narens is Professor of Cognitive Science at the University of California, Irvine. He is the author of Abstract Measurement Theory (MIT, 1985) and Introduction to the Theories of Measurement and Meaningfulness and the Use of Invariance in Science (Lawrence Erlbaum, 2007). Brian Skyrms is Distinguished Professor of Logic and Philosophy of Science and Economics at the University of California, Irvine. His interests include the evolution of conventions, the social contract, inductive logic, decision theory, rational deliberation, the metaphysics of logical atomism, causality, and truth. He is the author of Signals: Evolution, Learning, and Information (OUP, 2010), From Zeno to Arbitrage: Essays on Quantity, Coherence, and Induction (OUP, 2012), and Social Dynamics (OUP, 2014).