5 Model Theory of Modal Logic
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Stone Coalgebras
Electronic Notes in Theoretical Computer Science 82 No. 1 (2003) URL: http://www.elsevier.nl/locate/entcs/volume82.html 21 pages Stone Coalgebras Clemens Kupke 1 Alexander Kurz 2 Yde Venema 3 Abstract In this paper we argue that the category of Stone spaces forms an interesting base category for coalgebras, in particular, if one considers the Vietoris functor as an analogue to the power set functor. We prove that the so-called descriptive general frames, which play a fundamental role in the semantics of modal logics, can be seen as Stone coalgebras in a natural way. This yields a duality between the category of modal algebras and that of coalgebras over the Vietoris functor. Building on this idea, we introduce the notion of a Vietoris polynomial functor over the category of Stone spaces. For each such functor T we establish a link between the category of T -sorted Boolean algebras with operators and the category of Stone coalgebras over T . Applications include a general theorem providing final coalgebras in the category of T -coalgebras. Key words: coalgebra, Stone spaces, Vietoris topology, modal logic, descriptive general frames, Kripke polynomial functors 1 Introduction Technically, every coalgebra is based on a carrier which itself is an object in the so-called base category. Most of the literature on coalgebras either focuses on Set as the base category, or takes a very general perspective, allowing arbitrary base categories, possibly restricted by some constraints. The aim of this paper is to argue that, besides Set, the category Stone of Stone spaces is of relevance as a base category. -
The Modal Logic of Potential Infinity, with an Application to Free Choice
The Modal Logic of Potential Infinity, With an Application to Free Choice Sequences Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Ethan Brauer, B.A. ∼6 6 Graduate Program in Philosophy The Ohio State University 2020 Dissertation Committee: Professor Stewart Shapiro, Co-adviser Professor Neil Tennant, Co-adviser Professor Chris Miller Professor Chris Pincock c Ethan Brauer, 2020 Abstract This dissertation is a study of potential infinity in mathematics and its contrast with actual infinity. Roughly, an actual infinity is a completed infinite totality. By contrast, a collection is potentially infinite when it is possible to expand it beyond any finite limit, despite not being a completed, actual infinite totality. The concept of potential infinity thus involves a notion of possibility. On this basis, recent progress has been made in giving an account of potential infinity using the resources of modal logic. Part I of this dissertation studies what the right modal logic is for reasoning about potential infinity. I begin Part I by rehearsing an argument|which is due to Linnebo and which I partially endorse|that the right modal logic is S4.2. Under this assumption, Linnebo has shown that a natural translation of non-modal first-order logic into modal first- order logic is sound and faithful. I argue that for the philosophical purposes at stake, the modal logic in question should be free and extend Linnebo's result to this setting. I then identify a limitation to the argument for S4.2 being the right modal logic for potential infinity. -
DRAFT: Final Version in Journal of Philosophical Logic Paul Hovda
Tensed mereology DRAFT: final version in Journal of Philosophical Logic Paul Hovda There are at least three main approaches to thinking about the way parthood logically interacts with time. Roughly: the eternalist perdurantist approach, on which the primary parthood relation is eternal and two-placed, and objects that persist persist by having temporal parts; the parameterist approach, on which the primary parthood relation is eternal and logically three-placed (x is part of y at t) and objects may or may not have temporal parts; and the tensed approach, on which the primary parthood relation is two-placed but (in many cases) temporary, in the sense that it may be that x is part of y, though x was not part of y. (These characterizations are brief; too brief, in fact, as our discussion will eventually show.) Orthogonally, there are different approaches to questions like Peter van Inwa- gen's \Special Composition Question" (SCQ): under what conditions do some objects compose something?1 (Let us, for the moment, work with an undefined notion of \compose;" we will get more precise later.) One central divide is be- tween those who answer the SCQ with \Under any conditions!" and those who disagree. In general, we can distinguish \plenitudinous" conceptions of compo- sition, that accept this answer, from \sparse" conceptions, that do not. (van Inwagen uses the term \universalist" where we use \plenitudinous.") A question closely related to the SCQ is: under what conditions do some objects compose more than one thing? We may distinguish “flat” conceptions of composition, on which the answer is \Under no conditions!" from others. -
Branching Time
24.244 Modal Logic, Fall 2009 Prof. Robert Stalnaker Lecture Notes 16: Branching Time Ordinary tense logic is a 'multi-modal logic', in which there are two (pairs of) modal operators: P/H and F/G. In the semantics, the accessibility relations, for past and future tenses, are interdefinable, so in effect there is only one accessibility relation in the semantics. However, P/H cannot be defined in terms of F/G. The expressive power of the language does not match the semantics in this case. But this is just a minimal multi-modal theory. The frame is a pair consisting of an accessibility relation and a set of points, representing moments of time. The two modal operators are defined on this one set. In the branching time theory, we have two different W's, in a way. We put together the basic tense logic, where the points are moments of time, with the modal logic, where they are possible worlds. But they're not independent of one another. In particular, unlike abstract modal semantics, where possible worlds are primitives, the possible worlds in the branching time theory are defined entities, and the accessibility relation is defined with respect to the structure of the possible worlds. In the pure, abstract theory, where possible worlds are primitives, to the extent that there is structure, the structure is defined in terms of the relation on these worlds. So the worlds themselves are points, the structure of the overall frame is given by the accessibility relation. In the branching time theory, the possible worlds are possible histories, which have a structure defined by a more basic frame, and the accessibility relation is defined in terms of that structure. -
29 Alethic Modal Logics and Semantics
29 Alethic Modal Logics and Semantics GERHARD SCHURZ 1 Introduction The first axiomatic development of modal logic was untertaken by C. I. Lewis in 1912. Being anticipated by H. McCall in 1880, Lewis tried to cure logic from the ‘paradoxes’ of extensional (i.e. truthfunctional) implication … (cf. Hughes and Cresswell 1968: 215). He introduced the stronger notion of strict implication <, which can be defined with help of a necessity operator ᮀ (for ‘it is neessary that:’) as follows: A < B iff ᮀ(A … B); in words, A strictly implies B iff A necessarily implies B (A, B, . for arbitrary sen- tences). The new primitive sentential operator ᮀ is intensional (non-truthfunctional): the truth value of A does not determine the truth-value of ᮀA. To demonstrate this it suf- fices to find two particular sentences p, q which agree in their truth value without that ᮀp and ᮀq agree in their truth-value. For example, it p = ‘the sun is identical with itself,’ and q = ‘the sun has nine planets,’ then p and q are both true, ᮀp is true, but ᮀq is false. The dual of the necessity-operator is the possibility operator ‡ (for ‘it is possible that:’) defined as follows: ‡A iff ÿᮀÿA; in words, A is possible iff A’s negation is not necessary. Alternatively, one might introduce ‡ as new primitive operator (this was Lewis’ choice in 1918) and define ᮀA as ÿ‡ÿA and A < B as ÿ‡(A ŸÿB). Lewis’ work cumulated in Lewis and Langford (1932), where the five axiomatic systems S1–S5 were introduced. -
What Is a Logic Translation? in Memoriam Joseph Goguen
, 1{29 c 2009 Birkh¨auserVerlag Basel/Switzerland What is a Logic Translation? In memoriam Joseph Goguen Till Mossakowski, R˘azvan Diaconescu and Andrzej Tarlecki Abstract. We study logic translations from an abstract perspective, with- out any commitment to the structure of sentences and the nature of logical entailment, which also means that we cover both proof-theoretic and model- theoretic entailment. We show how logic translations induce notions of logical expressiveness, consistency strength and sublogic, leading to an explanation of paradoxes that have been described in the literature. Connectives and quanti- fiers, although not present in the definition of logic and logic translation, can be recovered by their abstract properties and are preserved and reflected by translations under suitable conditions. 1. Introduction The development of a notion of logic translation presupposes the development of a notion of logic. Logic has been characterised as the study of sound reasoning, of what follows from what. Hence, the notion of logical consequence is central. It can be obtained in two complementary ways: via the model-theoretic notion of satisfaction in a model and via the proof-theoretic notion of derivation according to proof rules. These notions can be captured in a completely abstract manner, avoiding any particular commitment to the nature of models, sentences, or rules. The paper [40], which is the predecessor of our current work, explains the notion of logic along these lines. Similarly, an abstract notion of logic translation can be developed, both at the model-theoretic and at the proof-theoretic level. A central question concern- ing such translations is their interaction with logical structure, such as given by logical connectives, and logical properties. -
Probabilistic Semantics for Modal Logic
Probabilistic Semantics for Modal Logic By Tamar Ariela Lando A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Philosophy in the Graduate Division of the University of California, Berkeley Committee in Charge: Paolo Mancosu (Co-Chair) Barry Stroud (Co-Chair) Christos Papadimitriou Spring, 2012 Abstract Probabilistic Semantics for Modal Logic by Tamar Ariela Lando Doctor of Philosophy in Philosophy University of California, Berkeley Professor Paolo Mancosu & Professor Barry Stroud, Co-Chairs We develop a probabilistic semantics for modal logic, which was introduced in recent years by Dana Scott. This semantics is intimately related to an older, topological semantics for modal logic developed by Tarski in the 1940’s. Instead of interpreting modal languages in topological spaces, as Tarski did, we interpret them in the Lebesgue measure algebra, or algebra of measurable subsets of the real interval, [0, 1], modulo sets of measure zero. In the probabilistic semantics, each formula is assigned to some element of the algebra, and acquires a corresponding probability (or measure) value. A formula is satisfed in a model over the algebra if it is assigned to the top element in the algebra—or, equivalently, has probability 1. The dissertation focuses on questions of completeness. We show that the propo- sitional modal logic, S4, is sound and complete for the probabilistic semantics (formally, S4 is sound and complete for the Lebesgue measure algebra). We then show that we can extend this semantics to more complex, multi-modal languages. In particular, we prove that the dynamic topological logic, S4C, is sound and com- plete for the probabilistic semantics (formally, S4C is sound and complete for the Lebesgue measure algebra with O-operators). -
Logic-Sensitivity of Aristotelian Diagrams in Non-Normal Modal Logics
axioms Article Logic-Sensitivity of Aristotelian Diagrams in Non-Normal Modal Logics Lorenz Demey 1,2 1 Center for Logic and Philosophy of Science, KU Leuven, 3000 Leuven, Belgium; [email protected] 2 KU Leuven Institute for Artificial Intelligence, KU Leuven, 3000 Leuven, Belgium Abstract: Aristotelian diagrams, such as the square of opposition, are well-known in the context of normal modal logics (i.e., systems of modal logic which can be given a relational semantics in terms of Kripke models). This paper studies Aristotelian diagrams for non-normal systems of modal logic (based on neighborhood semantics, a topologically inspired generalization of relational semantics). In particular, we investigate the phenomenon of logic-sensitivity of Aristotelian diagrams. We distin- guish between four different types of logic-sensitivity, viz. with respect to (i) Aristotelian families, (ii) logical equivalence of formulas, (iii) contingency of formulas, and (iv) Boolean subfamilies of a given Aristotelian family. We provide concrete examples of Aristotelian diagrams that illustrate these four types of logic-sensitivity in the realm of normal modal logic. Next, we discuss more subtle examples of Aristotelian diagrams, which are not sensitive with respect to normal modal logics, but which nevertheless turn out to be highly logic-sensitive once we turn to non-normal systems of modal logic. Keywords: Aristotelian diagram; non-normal modal logic; square of opposition; logical geometry; neighborhood semantics; bitstring semantics MSC: 03B45; 03A05 Citation: Demey, L. Logic-Sensitivity of Aristotelian Diagrams in Non-Normal Modal Logics. Axioms 2021, 10, 128. https://doi.org/ 1. Introduction 10.3390/axioms10030128 Aristotelian diagrams, such as the so-called square of opposition, visualize a number Academic Editor: Radko Mesiar of formulas from some logical system, as well as certain logical relations holding between them. -
Boxes and Diamonds: an Open Introduction to Modal Logic
Boxes and Diamonds An Open Introduction to Modal Logic F19 Boxes and Diamonds The Open Logic Project Instigator Richard Zach, University of Calgary Editorial Board Aldo Antonelli,y University of California, Davis Andrew Arana, Université de Lorraine Jeremy Avigad, Carnegie Mellon University Tim Button, University College London Walter Dean, University of Warwick Gillian Russell, Dianoia Institute of Philosophy Nicole Wyatt, University of Calgary Audrey Yap, University of Victoria Contributors Samara Burns, Columbia University Dana Hägg, University of Calgary Zesen Qian, Carnegie Mellon University Boxes and Diamonds An Open Introduction to Modal Logic Remixed by Richard Zach Fall 2019 The Open Logic Project would like to acknowledge the gener- ous support of the Taylor Institute of Teaching and Learning of the University of Calgary, and the Alberta Open Educational Re- sources (ABOER) Initiative, which is made possible through an investment from the Alberta government. Cover illustrations by Matthew Leadbeater, used under a Cre- ative Commons Attribution-NonCommercial 4.0 International Li- cense. Typeset in Baskervald X and Nimbus Sans by LATEX. This version of Boxes and Diamonds is revision ed40131 (2021-07- 11), with content generated from Open Logic Text revision a36bf42 (2021-09-21). Free download at: https://bd.openlogicproject.org/ Boxes and Diamonds by Richard Zach is licensed under a Creative Commons At- tribution 4.0 International License. It is based on The Open Logic Text by the Open Logic Project, used under a Cre- ative Commons Attribution 4.0 Interna- tional License. Contents Preface xi Introduction xii I Normal Modal Logics1 1 Syntax and Semantics2 1.1 Introduction.................... -
Duality Theory, Canonical Extensions and Abstract Algebraic Logic
DUALITY THEORY, CANONICAL EXTENSIONS AND ABSTRACT ALGEBRAIC LOGIC MAR´IA ESTEBAN GARC´IA Resumen. El principal objetivo de nuestra propuesta es mostrar que la L´ogicaAlgebraica Abstracta nos proporciona el marco te´oricoadecuado para desarrollar una teor´ıauniforme de la dualidad y de las extensiones can´onicaspara l´ogicasno clsicas. Una teor´ıatal sirve, en esencia, para definir de manera uniforme sem´anticas referenciales (e.g. relacionales, al estilo Kripke) de un amplio rango de l´ogicaspara las cuales se conoce una sem´antica algebraica. Abstract. The main goal of our proposal is to show that Abstract Al- gebraic Logic provides the appropriate theoretical framework for devel- oping a uniform duality and canonical extensions theory for non-classical logics. Such theory serves, in essence, to define uniformly referential (e.g. relational, Kripke-style) semantics of a wide range of logics for which an algebraic semantics is already known. 1. Abstract Algebraic Logic Our work is located in the field of Abstract Algebraic Logic (AAL for short). Our main reference for AAL is the survey by Font, Jansana and Pigozzi [14]. We introduce now the definition of logic adopted in AAL. It consists, essentially, on regarding logic as something concerning validity of inferences, instead of validity of formuli. Let L be a logical language, defined as usual from a countably infinite set of propositional variables V ar. We denote by F mL the collection of all L -formulas. When we consider the connectives as the operation symbols of an algebraic similarity type, we obtain the algebra of terms, which is the absolutely free algebra of type L over a denumerable set of generators V ar. -
Tense Or Temporal Logic Gives a Glimpse of a Number of Related F-Urther Topics
TI1is introduction provi'des some motivational and historical background. Basic fonnal issues of propositional tense logic are treated in Section 2. Section 3 12 Tense or Temporal Logic gives a glimpse of a number of related f-urther topics. 1.1 Motivation and Terminology Thomas Miiller Arthur Prior, who initiated the fonnal study of the logic of lime in the 1950s, called lus logic tense logic to reflect his underlying motivation: to advance the philosophy of time by establishing formal systems that treat the tenses of nat \lrallanguages like English as sentence-modifying operators. While many other Chapter Overview formal approaches to temporal issues have been proposed h1 the meantime, Pri orean tense logic is still the natural starting point. Prior introduced four tense operatm·s that are traditionally v.rritten as follows: 1. Introduction 324 1.1 Motiv<Jtion and Terminology 325 1.2 Tense Logic and the History of Formal Modal Logic 326 P it ·was the case that (Past) 2. Basic Formal Tense Logic 327 H it has always been the case that 2.1 Priorean (Past, Future) Tense Logic 328 F it will be the case that (Future) G it is always going to be the case that 2.1.1 The Minimal Tense Logic K1 330 2.1 .2 Frame Conditions 332 2.1.3 The Semantics of the Future Operator 337 Tims, a sentence in the past tense like 'Jolm was happy' is analysed as a temporal 2.1.4 The lndexicai'Now' 342 modification of the sentence 'John is happy' via the operator 'it was the case thai:', 2.1.5 Metric Operators and At1 343 and can be formally expressed as 'P HappyO'olm)'. -
First-Order Resolution Methods for Modal Logics*
First-Order Resolution Methods for Modal Logics⋆ R. A. Schmidt1 and U. Hustadt2 1 The University of Manchester, UK, [email protected] 2 University of Liverpool, UK, [email protected] Abstract. In this paper we give an overview of results for modal logic which can be shown using techniques and methods from first-order logic and resolution. Because of the breadth of the area and the many appli- cations we focus on the use of first-order resolution methods for modal logics. In addition to traditional propositional modal logics we consider more expressive PDL-like dynamic modal logics which are closely related to description logics. Without going into too much detail, we survey dif- ferent ways of translating modal logics into first-order logic, we explore different ways of using first-order resolution theorem provers, and we discuss a variety of results which have been obtained in the setting of first-order resolution. 1 Introduction The main motivation for reducing problems in one logic (the source logic) to ‘equivalent’ problems in another logic (the target logic) is to exploit results of the target logic to draw some conclusions about the initial problems and use existing methods and tools of the target logic for the purpose of solving prob- lems in the source logic. Reduction of modal logic problems to first-order logic is the pertinent case considered in this paper. There are good reasons for following this approach. First, a plethora of results on first-order logic and subclasses of it are available, including (un)decidability results, complexity results, correctness results for a wide range of calculi for first-order logic, and results on practical aspects and optimisation of the implementation of these calculi.