Brian Skyrms presents a set of influential essays on the nature of quantity, probability, coherence, and induction. The first part explores the nature of quantity and includes essays on tractarian nominalism, combinatorial possibility, and coherence. Part Two proceeds to examine coherent updating of degrees of belief in various learning situations. Finally, in Part Three, Skyrms develops an account of aspects of inductive reasoning, which proceeds from specific problems to general considerations. These essays span the breadth of Skyrms's illustrious career and will be essential reading for scholars and advanced students in philosophy of science and formal epistemology.