Inquisitive Semantics and Intermediate Logics
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Inquisitive Semantics and Intermediate Logics. MSc Thesis (Afstudeerscriptie) written by Ivano A. Ciardelli (born February 3rd, 1985 in Sesto san Giovanni, Italy) under the supervision of Prof Dr Jeroen Groenendijk, Prof Dr Dick de Jongh, and Dr Floris Roelofsen, and submitted to the Board of Examiners in partial fulfillment of the requirements for the degree of MSc in Logic at the Universiteit van Amsterdam. Date of the public defense: Members of the Thesis Committee: September 3, 2009 Prof Dr Johan van Benthem Prof Dr Jeroen Groenendijk Dr Rosalie Iemhoff Prof Dr Dick de Jongh Dr Floris Roelofsen Dr Yde Venema [::: ] Sono allora un soldatino di piombo appeso a un filo sul mare aperto I miei pensieri passano come velieri [::: ] Leonardo Martellini, Velieri To my schoolteacher Mauro, who taught me how to doubt i Contents Acknowledgements............................. iv Overview of the thesis...........................v 1 An introduction to inquisitive semantics1 1.1 Information states and the classical update perspective......1 1.2 Limitations of the classical picture.................2 1.3 The inquisitive programme: propositions as proposals......3 1.4 Sources of inquisitiveness: questions, disjunctions and indefinites4 1.5 Historical notes............................5 2 Propositional inquisitive semantics7 2.1 Propositional inquisitive semantics and its properties.......7 2.1.1 Indices, States, and Support.................7 2.1.2 Inquisitive meanings.....................9 2.1.3 Inquisitiveness and Informativeness............. 12 2.2 Inquisitive semantics and intuitionistic Kripke semantics..... 15 2.3 Inquisitive semantics over an arbitrary common ground..... 16 2.4 Support as `knowing how'...................... 18 2.5 Expressive completeness and disjunctive normal form....... 19 3 Inquisitive logic 22 3.1 Inquisitive Logic........................... 22 3.1.1 Definitions and basic properties............... 22 3.1.2 Disjunction Property, Deduction Theorem, and Compact- ness.............................. 23 3.2 Axiomatizing InqL .......................... 25 3.2.1 Intermediate logics and negative variants......... 26 3.2.2 Completeness by canonical model.............. 30 3.2.3 Completeness via disjunctive-negative translation..... 39 3.3 InqL as the disjunctive-negative fragment of IPL.......... 41 3.4 Schematic Fragment of Inquisitive Logic.............. 44 3.4.1 Medvedev logic........................ 44 3.4.2 Sch(InqL)=ML ........................ 45 3.4.3 Characterization of the intermediate logics whose negative variant is InqL ........................ 46 ii 3.4.4 More on Medvedev logic................... 48 3.5 Independence of the connectives.................. 52 4 The inquisitive hierarchy 55 4.1 Generalizing the pair semantics................... 55 4.2 Axiomatizing the inquisitive hierarchy............... 58 4.3 A Plea for the Generalized Semantics................ 59 5 Intermediate logics with negative atoms 61 5.1 Negative closure of intermediate logics............... 62 5.2 Stability of intermediate logics................... 64 6 First-order inquisitive semantics 77 6.1 First-order inquisitive semantics and the maximality problem.. 77 6.2 Propositional possibility semantics................. 81 6.2.1 Propositions......................... 81 6.2.2 Resolutions.......................... 83 6.2.3 Strong entailment...................... 85 6.2.4 Disjunctive normal form and expressive completeness... 86 6.2.5 Inquisitiveness, informativeness, suggestiveness...... 87 6.2.6 Assertions, questions, and conjectures........... 90 6.2.7 Axiomatizing strong entailment............... 94 6.3 First-order possibility semantics................... 97 6.3.1 Propositions......................... 97 6.3.2 Entailment and strong entailment............. 99 6.3.3 Resolutions.......................... 101 6.3.4 Inquisitiveness, informativeness, suggestiveness...... 103 6.3.5 Assertions, questions, and conjectures........... 104 6.4 Might meets the logical constants.................. 106 6.5 An assessment of possibility semantics............... 109 6.6 Notes on first-order inquisitive logic................ 110 6.6.1 Definition and basic properties............... 110 6.6.2 IQL ⊆ InqQL ⊆ CQL ..................... 111 6.6.3 Correspondence theorem................... 114 7 Conclusions 117 References 118 iii Acknowledgements My gratitude goes in the first place to my supervisors, thanks to whom the preparation of this thesis has been a truly exciting, interesting and fun experi- ence. Thanks to Jeroen Groenendijk for introducing me to the ideas of inquisitive semantics, for stimulating and encouraging my work on it, and for actively considering and criticizing each of the preliminary versions of the ideas contained here: rarely have I met such an affable and open-minded person. Thanks to Dick de Jongh for his experienced and patient supervision, as well as for his wise advice and his support in my many moments of doubt and indecision. Thanks to Floris Roelofsen for a number of things: for several brilliant in- tuitions that were crucial to the development of the proof presented in section 3.2.2; for patiently answering a horde of silly questions that I have been gen- erating in virtue of my inexperience in scientific writing; but especially for the many, many pleasant hours we spent together discussing, attempting proofs, laughing, planning, eating, and climbing trees. Also, thanks to the supernatural room on the top floor of the philosophy department for incubating so many ideas: its contribution to the present thesis is invaluable. The ILLC has provided me with an extraordinarily rich, diverse and highly stimulating scientific environment. For this experience I am grateful to all the ILLC staff and to my fellow master's students, but special thanks I owe to: Yde Venema, for the clarity and pleasantness of his teaching; to In´esCrespo, for excellently sustaining the role of personal counselor I saddled her with; to Matthew Wampler-Doty, for crucially pointing out the existence of a similarity between inquisitive semantics and Medvedev frames; to Lex Hendriks, for con- tributing useful information and references; and, last but not least, to Benedikt L¨owe and Tanja Kassenaar, for the truly admirable organization of the program, which made everything easy even for a complete bureaucratic bungler like me. I also wish to thank three persons who have been especially influential in my own cultural and scientific growth, namely my schoolteacher Mauro Pellegrinelli and my university professors Bruno Franchi and Simone Martini. Finally, I would like to thank the Dutch Ministry of Education and the Beth Foundation for their generous financial support, which allowed me to con- centrate exclusively on my studies in these two years, and the Philosophy of Language Group directed by Paul Dekker and Martin Stokhof for funding my trip to the conference TARK at Stanford, thus giving me the opportunity to present some of the results contained in this thesis. iv Overview of the thesis The present thesis is concerned with inquisitive semantics and its logic. In- quisitive semantics is a system (or rather a class of systems) for modelling the effect of utterances in a cooperative dialogue; the crucial feature of inquisitive semantics is that it regards propositions as real proposals of one or more pos- sible updates for the common ground of a conversation, thus allowing for the representation of both inquisitive and informative content as two aspects of a unique notion of meaning. We start with a general overview of the structure and the contents of the thesis. Chapter 1: an introduction to inquisitive semantics. We introduce the reader to the ideas that motivate and guide the development of an inquisitive semantics. We first mention a traditional approach to the modelling of the exchange of information in a dialogue. We then illustrate a different perspec- tive on cooperative information exchange, namely the propositions-as-proposals view which informs the construction of inquisitive semantics. We conclude the chapter with some historical notes, clarifying how the present thesis relates to previous and ongoing work on the subject. Chapter 2: propositional inquisitive semantics. We set out to imple- ment the ideas expounded in the previous chapter for a propositional language. We evaluate formulas over sets of valuations, conceived of as information states. The semantics is based upon the relation of support between states and propo- sitional formulas: via the notion of support, we associate each formula with a set of possibilities, defined as maximal states supporting the formula. This set of possibilities represents the proposal put forward by a formula. We identify two effects of a proposal: an informative effect consisting in the suggestion to eliminate some possible worlds from the common ground, and an inquisitive effect consisting in the specification of alternative updates. We define assertions and questions as formulas that serve only one of these purposes and discuss the properties of these classes of formulas, in particular showing that each formula can always be decomposed into a question and an assertion, its assertive part coinciding with its classical meaning. We discuss several other properties of the semantics, such as expressive com- pleteness and normal form results, point out a tight connection linking inquisi- tive semantics to intuitionistic Kripke semantics, and suggest an intuitive inter- pretation of the notion of support as `knowing how'. Chapter 3: inquisitive logic.