When I was an undergraduate student decades ago, one of the courses I took to meet the required number of upper division credit hours in philosophy was on epistemology, the study of knowledge: How is it acquired? What is the structure of knowledge? How is knowledge communicated? How does knowledge relate to belief? How is the claim of knowledge or belief justified? The approach was classical: the study of Aristotle, Thomas Aquinas, Rene Descartes, Immanuel Kant, David Hume, and John Locke, and other great thinkers. The importance of epistemology in philosophy is that it is inextricably coupled with the study of metaphysics and ontology.

Formal epistemology extends the study of epistemology beyond its classical foundations. It is a relatively recent phenomenon, having arisen in the past 25 years. A large fraction of the developers in formal epistemology came from areas other than philosophy, such as economics, game theory, computer science, simulation and modeling, and statistics. Many of the principal questions and problems arising in all of these disciplines were epistemological: that of knowing (by individuals or groups), the structure of this knowledge, how this knowledge is acquired, the degree to which the individuals or groups are convinced of the adequacy and veracity of the knowledge, and how this knowledge or strong belief can lead to choices and actions.

Because of the relative youth of this segment of epistemological studies, the editors of this volume perceived a need for a single volume of nonbook publications upon which formal epistemology has been based. If individuals were to attempt to gather them all for their own study, it would be a daunting task. Forty-three papers were assembled as individual chapters in over 930 pages of text. Securing the reprint rights from the original publishers must have been a challenging task.

After an introductory paper describing the organization of the book and presenting an overview of formal epistemology, the remaining 42 papers are organized into five parts: (1) “Bayesian Epistemology” (papers 2 to 11), (2) “Belief Change” (papers 12 to 17), (3) “Decision Theory” (papers 18 to 24), (4) “Logics of Knowledge and Belief” (papers 25 to 34), and “Interactive Epistemology” (papers 35 to 43). The first paper in each part was written by the editors and is an introduction to the topic of the part. Each short essay ends with a section with suggestions for further reading of other longer book-length works. These contributions are very useful in orienting the reader to the other papers in the part.

There are two principal notions that characterize formal epistemology and that pervade the book: agency and interaction. The emphasis on these two properties is important. The notions describe a shift from the external world and from a more passive view of the knower in classical epistemology to actors who know and believe, who communicate knowledge among themselves, and who make decisions and take actions based on the acquired knowledge. Action as part of the knowing process is more prominent and explicit than in the classical sense of epistemology. Another pervasive concept applied throughout is the statistical estimation of the extent of knowing or believing. No knowledge is perfect. No belief in a proposition is hard and fast. Logic is not necessarily strictly Aristotelian. The lack of crispness in knowledge and belief has implications in the interaction of agents, decision making, and taking action. All of these are quite relevant to economic and social system modelers, to ontologists describing artifacts and events, and to game theorists.

This book has been several years in the making. The principal editor, Horacio Arló-Costa, died before the project was completed. The other editors completed the project successfully--a task well done.