Epistemic Modality, Mind, and Mathematics
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Epistemic Modality, Mind, and Mathematics Hasen Khudairi June 20, 2017 c Hasen Khudairi 2017, 2021 All rights reserved. 1 Abstract This book concerns the foundations of epistemic modality. I examine the nature of epistemic modality, when the modal operator is interpreted as con- cerning both apriority and conceivability, as well as states of knowledge and belief. The book demonstrates how epistemic modality relates to the compu- tational theory of mind; metaphysical modality; the types of mathematical modality; to the epistemic status of undecidable propositions and abstraction principles in the philosophy of mathematics; to the modal profile of rational propositional intuition; and to the types of intention, when the latter is in- terpreted as a modal mental state. Each essay is informed by epistemic logic, intensional semantics, hyperintensional semantics, modal and cylindric alge- bra or coalgebra, modal fixpoint logic, correspondence theory, or automata theory. The book’s original contributions include theories of: (i) epistemic modal algebras and coalgebras; (ii) cognitivism about epistemic modality; (iii) two-dimensional truthmaker semantics, and interpretations thereof; (iv) the ground-theoretic ontology of consciousness; (v) fixed-points in vague- ness and a novel approach to conditions of self-knowledge in the setting of the modal µ-calculus; (vi) the modal foundations of mathematical platon- ism; (vii) a solution to the Julius Caesar problem based on metaphysical definitions availing of notions of ground and essence; (viii) the application of epistemic two-dimensional semantics to the epistemology of mathematics; (ix) a modal logic for rational intuition; and (x) a novel epistemicist solution to Curry’s paradox. 2 Acknowledgements From 2014 to 2017, I was a Ph.D. Student at the Arché Philosophical Re- search Centre for Logic, Language, Metaphysics and Epistemology at the University of St Andrews. St Andrews is an ideal place to live and work. At Arché, I was supported by a St Leonard’s College (SASP) Research Scholar- ship, for which I record my gratitude. This book is a revised version of my dissertation. The dissertation was written between the foregoing years, and revised in the years that followed. For comments which lead to revisions to individual chapters, I am grateful to Josh Dever, Peter Milne, and Gabriel Uzquiano. For productive conversations at Arché, I am grateful to Mark Bowker, Sarah Broadie, Aaron Cotnoir, Federico Faroldi, Katherine Hawley, Patrik Hummel, Ryo Ito, Bruno Jacinto, Li Kang, Kris Kersa, Martin Lipman, Poppy Mankowitz, Matthew McKeever, Daniel Nolan, Laurie Paul, Andrew Peet, Stephen Read, Justin Snedegar, Mark Thakkar, Jens Timmermann, Michael Traynor, Brian Weatherson, and Erik Wielenberg. For her adminis- trative assistance, I am grateful to Lynn Hynd. For productive discussion at conferences, workshops, et al., I am grateful to Jody Azzouni, Ralf Bader, George Bealer, Jacob Berger, Corine Besson, Ned Block, Susanne Bobzien, Otavio Bueno, Fabrizio Cariani, David Chalmers, Roy Cook, Paul Linton Cowie, Brian Epstein, Delia Graff Fara, Kit Fine, Peter Fritz, Zachary Gartenberg, Nemira Gasiunas, Tamar Gendler, Sandy Goldberg, Sally Haslanger, Benj Hellie, Christopher Hill, Sean Kelly, Uriah Kriegel, Maria Lasonen-Aarnio, Anita Leirfall, Hannes Leitgeb, Mary Leng, Stephan Leuenberger, Øystein Linnebo, Julien Murzi, Myrto Mylopoulos, Bryan Pickel, Agustin Rayo, Mark Richard, David Ripley, Sonia Roca-Royes, Gideon Rosen, David Rosenthal, Marcus Rossberg, Ian Rumfitt, Sarah Sawyer, Claudia Schaer, Wolfgang Schwarz, Erica Shumener, Jonathan Simon, Robert Stalnaker, Ravi Tharakan, Achille Varzi, Katja Vogt, Robbie Williams, Tim- 3 othy Williamson, Jessica Wilson, Keith Wilson, Crispin Wright, Stephen Yablo, and Seth Yalcin. From 2005 to 2008, I was an honors undergraduate in philosophy at Johns Hopkins University. For their encouragement and example, I am grateful to Michael Williams, Hent de Vries, Meredith Williams, Dean Moyar, and Maura Tumulty. For his friendship and for visits at the beginning and end of the time this dissertation was written, I am grateful to Armand Leblois. For their unwavering support of my endeavors over the years, I am grateful to my parents. The book is dedicated to Alison Bowen. Chapter 6 has been published as "Grounding, Conceivability, and the Mind-Body Problem" in Synthese 195 (2):919-926 (2018), doi:10.1007/s11229- 016-1254-2. Chapter 8 has been published as "Modal Ω-Logic: Automata, Neo-Logicism, and Set-Theoretic Realism" in Don Berkich and Matteo Vin- cenzo d’Alfonso (eds.), On the Cognitive, Ethical, and Scientific Dimensions of Artificial Intelligence – Themes from IACAP 2016, Springer (2019). 4 Table of Contents 1. Methodological Forward (p. 10) Part I: A Framework for Epistemic Modality 2. Modal Cognitivism and Modal Expressivism (p. 23) 2.1 The Hybrid Proposal 2.1.1 Epistemic Modal Algebra 2.1.2 Modal Coalgebraic Automata 2.2 Material Adequacy 2.3 Expressivist Semantics for Epistemic Possibility 2.4 Modal Expressivism and the Philosophy of Mathematics 2.5 Concluding Remarks 3. Cognitivism about Epistemic Modality (p. 43) 3.1 Introduction 3.2 An Abstraction Principle for Epistemic Intensions 3.3 Examples in Philosophy and Cognitive Science 3.4 Objections and Replies 3.5 Concluding Remarks 4. Non-Transitive Self-Knowledge: Luminosity via Modal µ-Automata (p. 56) Part II: Conceivability and Metaphysical Possibility 5. Conceivability and Haecceitism (p. 63) 5 5.1 Introduction 5.2 Super-Rigidity 5.3 Two Dogmas of Semantic Rationalism 5.3.1 The First Dogma 5.3.2 The Second Dogma 5.3.2.1 The Julius Caesar Problem 5.3.3 Mereological Parthood 5.3.4 Summary 5.4 Determinacy and Consistency 5.5 Concluding Remarks 6. Grounding, Conceivability, and the Mind-Body Problem (p. 81) Part III: Epistemic Modality and the Philosophy of Mathemat- ics 7. Epistemic Modality, Necessitism, and Abstractionism (p. 91) 7.1 Introduction 7.2 The Abstractionist Foundations of Mathematics 7.3 Abstraction and Necessitism 7.3.1 Hale and Wright’s Arguments against Necessitism 7.3.2 Hale on the Necessary Being of Purely General Properties and Objects 7.3.2.1 Objections 7.3.3 Cardinality and Intensionality 7.4 Epistemic Modality, Metaphysical Modality, and Epistemic Utility and Entitlement 7.5 Concluding Remarks 8. Ω-Logicism: Automata, Neo-logicism, and Set-theoretic Realism (p. 113) 8.1. Introduction 8.2 Definitions 6 8.2.1 Axioms 8.2.2 Large Cardinals 8.2.3 Ω-Logic 8.3 Discussion 8.3.1 Neo-Logicism 8.3.2 Set-theoretic Realism 8.4 Concluding Remarks 9. Epistemic Modality and Absolute Decidability (p. 129) 9.1 Mathematical Modality 9.1.1 Metaphysical Mathematical Modality 9.1.2 Epistemic Mathematical Modality 9.1.3 Interaction 9.1.4 Modal Axioms 9.2 Departures from Precedent 9.3 Knowledge of Absolute Decidability 9.4 Concluding Remarks 10. Grothendieck Universes, and Indefinite Extensibility (p. 141) 10.1 Introduction 10.2 Indefinite Extensibility in Set Theory: Modal and Extensional Approaches 10.3 Grothendieck Universes 10.4 Modal Coalgebraic Automata and Indefinite Extensibility 10.5 Concluding Remarks 11. A Modal Logic for Gödelian Intuition (p. 156) 11.1 Introduction 11.2 Rational Intuition as Cognitive Phenomenology 11.3 Modalized Rational Intuition and Conceptual Elucidation 7 11.4 Concluding Remarks 12. An Epistemicist Solution to Curry’s Paradox (p. 168) 12.1 Scharp’s Replacement Theory 12.1.1 Properties of Ascending and Descending Truth 12.1.2 Scharp’s Theory: ADT 12.1.3 Semantics for ADT 12.2 New Extensions of ADT 12.2.1 First Extension: The Preface Paradox 12.2.2 Second Extension: Absolute Generality 12.2.3 Third Extension: Probabilistic Self-reference 12.2.4 Fourth Extension: The Sorites Paradox 12.3 Issues for ADT 12.3.1 Issue 1: Revenge Paradoxes 12.3.2 Issue 2: Validity 12.3.3 Issue 3: Hybrid Principles and Compositionality 12.3.4 Issue 4: ADT and Indeterminacy 12.3.5 Issue 5: Descending Truth, Ascending Truth, and Objectivity 12.3.6 Issue 6: Paradox, Sense, and Signification 12.4 Epistemicism and Alethic Paradox 12.5 Concluding Remarks Part IV: Epistemic Modality, Intention, and Decision Theory 13. Two-Dimensional Truthmaker Semantics (p. 189) 13.1. Introduction 13.2 Two-Dimensional Truthmaker Semantics 13.2.1 Intensional Semantics 13.2.2 Truthmaker Semantics 13.2.3 Two-Dimensional Truthmaker Semantics 8 13.3 New Interpretations 13.3.1 Fundamental and Derivative Truths 13.3.2 Decision Theory 13.3.3 Intentional Action 13.4 Concluding Remarks 14. Epistemic Modality, Intention, and Decision Theory (p. 205) 14.1 Introduction 14.2 The Modes of Intention 14.2.1 Intention-in-Action 14.2.2 Intention-with-which 14.2.3 Intention-for-the-Future 14.3 Intention in Decision Theory 14.4 Concluding Remarks Bibliography (p. 214) 9 Chapter 1 Methodological Forward This book concerns the foundations of epistemic modality. The work aims to advance our present understanding of the defining contours of epistemic modal space. I endeavor, then, to develop the theory of epistemic modal- ity, by accounting for its interaction with metaphysical modality; the types of mathematical modality; the epistemic status of undecidable propositions and abstraction principles in the philosophy of mathematics; the modal pro- file of rational propositional intuition; and the types of intention, when the latter is interpreted as a modal mental state. In each chapter, I examine the philosophical significance of the foregoing, by demonstrating its import to a number of previously intransigent philosophical issues. In Section 1, I provide a summary of each of the chapters. In Section 2, I examine the limits of competing proposals in the literature, and outline the need for a new approach. 1.1 Chapter Summary In Chapter 2, I provide a mathematically tractable background against which to model both modal cognitivism and modal expressivism. I argue that epis- temic modal algebras, endowed with a hyperintensional truthmaker seman- tics, comprise a materially adequate fragment of the language of thought.