Belief Revision About Logic

Abstract

In both popular culture and academic philosophy, logic is often treated as the foundation of “good” reasoning. A rational thinker (so the story goes) should form and revise their beliefs according to the laws of logic. However, in recent years, there has been substantial disagreement among philosophers regarding which principles of logic are correct. This disagreement, in turn, has naturally led to cases of belief revision about logic, whereby an individual changes their mind about which principles of logic they accept. The fact that the discipline of philosophy is now filled with (rational, intelligent) people who have revised their beliefs about logic raises an obvious but rarely discussed question: If logic is supposed to guide rational belief revision, what guides rational belief revision about logic? My dissertation seeks to provide a first step towards answering this question. The project is divided into three parts, plus an introduction that lays out my goals and methodology in detail. In Part I, I examine some technical and philosophical problems regarding how logics are classified. In Part II, I develop several interrelated belief revision frameworks that fall under the AGM belief revision tradition, the most influential tradition in the literature. In Part III, I develop a modal framework that is expressive enough to characterize the AGM systems of Part II, and I use this framework to show how these systems are subject to the problems discussed in Part I. The main product of this thesis is a collection of versatile formal frameworks that model belief revision about principles of logic. These frameworks describe structured procedures for belief revision that follow plausible rationality principles, thereby offering an answer to the question “What guides rational belief revision about logic?” I conclude the thesis by reflecting on the philosophical significance of some results proven in Part III and by discussing some open questions for future research.