Modal Logic

Edited by Matteo Pascucci (Slovak Academy of Sciences, Central European University)
About this topic
Summary Modal logic is the study of the deductive behavior of concepts like "necessary", "possible", "contingent", etc.  Nowadays it encompasses several areas of research at the intersection of philosophy, mathematics and computer science.
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  1. Modal Logic: The System S5.Gabriel Andrus - manuscript
    A brief overview of the system S5 in modal logic as defined by Brian F. Chellas, author of "Modal Logic: An Introduction." The history and usage of modal logic are given mention, along with some applications. Very much a draft. Written for PhileInSophia on July 5, 2021.
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  2. The Logic of Logical Necessity.Andrew Bacon & Kit Fine - manuscript
    Prior to Kripke's seminal work on the semantics of modal logic, McKinsey offered an alternative interpretation of the necessity operator, inspired by the Bolzano-Tarski notion of logical truth. According to this interpretation, `it is necessary that A' is true just in case every sentence with the same logical form as A is true. In our paper, we investigate this interpretation of the modal operator, resolving some technical questions, and relating it to the logical interpretation of modality and some views in (...)
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  3. Modeling Future Indeterminacy in Possibility Semantics.Fabrizio Cariani - manuscript
    I consider the application of possibility semantics to the modeling of the indeterminacy of the future. I argue that interesting problems arise in connection to the addition of object-language determinacy operator. I show that adding a two-dimensional layer to possibility semantics can help solve these problems.
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  4. Cathoristic Logic.Richard Evans - manuscript
    Cathoristic logic is a multi-modal logic where negation is replaced by a novel operator allowing the expression of incompatible sentences. We present the syntax and semantics of the logic including complete proof rules, and establish a number of results such as compactness, a semantic characterisa- tion of elementary equivalence, the existence of a quadratic-time decision pro- cedure, and Brandom’s incompatibility semantics property. We demonstrate the usefulness of the logic as a language for knowledge representation.
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  5. We Belong Together? A Plea for Modesty in Modal Plural Logic.Simon Hewitt - manuscript
    It is often assumed that pluralities are rigid, in the sense of having all and only their actual members necessarily. This assumption is operative in standard approaches to modal plural logic. I argue that a sceptical approach towards the assumption is warranted.
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  6. A Fundamental Non-Classical Logic.Wesley Holliday - manuscript
    We give a proof-theoretic as well as a semantic characterization of a logic in the signature with conjunction, disjunction, negation, and the universal and existential quantifiers that we suggest has a certain fundamental status. We present a Fitch-style natural deduction system for the logic that contains only the introduction and elimination rules for the logical constants. From this starting point, if one adds the rule that Fitch called Reiteration, one obtains a proof system for intuitionistic logic in the given signature; (...)
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  7. A Modal Logic for Gödelian Intuition.Hasen Khudairi - manuscript
    This essay aims to provide a modal logic for rational intuition. Similarly to treatments of the property of knowledge in epistemic logic, I argue that rational intuition can be codified by a modal operator governed by the axioms of a dynamic provability logic, which embeds GL within the modal $\mu$-calculus. Via correspondence results between modal logic and the bisimulation-invariant fragment of second-order logic, a precise translation can then be provided between the notion of 'intuition-of', i.e., the cognitive phenomenal properties of (...)
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  8. Montague's Paradox Without Necessitation.T. Parent -
    Some such as Dean (2014) suggest that Montague's paradox requires the necessitation rule, and that the use of the rule in such a context is contentious. But here, I show that the paradox arises independently of the necessitation rule. A derivation of the paradox is given in modal system T without deploying necessitation; a necessitation-free derivation is also formulated in a significantly weaker system.
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  9. How Gödelian Ontological Arguments Fail.Matthew Parker - manuscript
    Ontological arguments like those of Gödel (1995) and Pruss (2009; 2012) rely on premises that initially seem plausible, but on closer scrutiny are not. The premises have modal import that is required for the arguments but is not immediately grasped on inspection, and which ultimately undermines the simpler logical intuitions that make the premises seem plausible. Furthermore, the notion of necessity that they involve goes unspecified, and yet must go beyond standard varieties of logical necessity. This leaves us little reason (...)
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  10. Modal Epistemology.Juhani Yli-Vakkuri & John Hawthorne - manuscript
    Some central epistemological notions are expressed by sentential operators O that entail the possibility of knowledge in the sense that 'Op' entails 'It is possible to know that p'. We call these modal-epistemological notions. Using apriority and being in a position to know as case studies, we argue that the logics of modal epistemological notions are extremely weak. In particular, their logics are not normal and do not include any closure principles.
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  11. Basic Concepts in Modal Logic.Edward N. Zalta - manuscript
    These lecture notes were composed while teaching a class at Stanford and studying the work of Brian Chellas (Modal Logic: An Introduction, Cambridge: Cambridge University Press, 1980), Robert Goldblatt (Logics of Time and Computation, Stanford: CSLI, 1987), George Hughes and Max Cresswell (An Introduction to Modal Logic, London: Methuen, 1968; A Companion to Modal Logic, London: Methuen, 1984), and E. J. Lemmon (An Introduction to Modal Logic, Oxford: Blackwell, 1977). The Chellas text influenced me the most, though the order of (...)
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  12. Chemical Possibility and Modal Semantics.Mark Sharlow - 2007
    This paper is a study of a distinctively chemical notion of possibility. This is the notion of possibility that occurs in chemical discourses when chemists speak of the possibility or impossibility of achieving a given result through chemical means. This notion pertains to the possibility of processes, not of compounds, so it differs from the kind of chemical possibility mentioned in Wittgenstein's Philosophical Investigations or the kinds discussed in the literature on Putnam's Twin Earth argument. I argue that this process-oriented (...)
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  13. A Lindström Theorem in Many-Valued Modal Logic Over a Finite MTL-Chain.Guillermo Badia & Grigory Olkhovikov - forthcoming - Fuzzy Sets and Systems.
    We consider a modal language over crisp frames and formulas evaluated on a finite MTL-chain (a linearly ordered commutative integral residuated lattice). We first show that the basic modal abstract logic with constants for the values of the MTL-chain is the maximal abstract logic satisfying Compactness, the Tarski Union Property and strong invariance for bisimulations. Finally, we improve this result by replacing the Tarski Union Property by a relativization property.
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  14. Logics of Formal Inconsistency Enriched with Replacement: An Algebraic and Modal Account.Walter Carnielli, Marcelo E. Coniglio & David Fuenmayor - forthcoming - Review of Symbolic Logic.
    One of the most expected properties of a logical system is that it can be algebraizable, in the sense that an algebraic counterpart of the deductive machinery could be found. Since the inception of da Costa's paraconsistent calculi, an algebraic equivalent for such systems have been searched. It is known that these systems are non self-extensional (i.e., they do not satisfy the replacement property). More than this, they are not algebraizable in the sense of Blok-Pigozzi. The same negative results hold (...)
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  15. In Search of Modal Hypodoxes Using Paradox Hypodox Duality.Peter Eldridge-Smith - forthcoming - Philosophia:1-20.
    The concept of hypodox is dual to the concept of paradox. Whereas a paradox is incompatibly overdetermined, a hypodox is underdetermined. Indeed, many particular paradoxes have dual hypodoxes. So, naively the dual of Russell’s Paradox is whether the set of all sets that are members of themselves is self-membered. The dual of the Liar Paradox is the Truth-teller, and a hypodoxical dual of the Heterological paradox is whether ‘autological’ is autological. I provide some analysis of the duality and I search (...)
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  16. Compatibility and Accessibility: Lattice Representations for Semantics of Non-Classical and Modal Logics.Wesley Holliday - forthcoming - In David Fernández Duque & Alessandra Palmigiano (eds.), Advances in Modal Logic, Vol. 14. London: College Publications.
    In this paper, we study three representations of lattices by means of a set with a binary relation of compatibility in the tradition of Ploščica. The standard representations of complete ortholattices and complete perfect Heyting algebras drop out as special cases of the first representation, while the second covers arbitrary complete lattices, as well as complete lattices equipped with a negation we call a protocomplementation. The third topological representation is a variant of that of Craig, Haviar, and Priestley. We then (...)
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  17. Inquisitive Intuitionistic Logic.Wesley H. Holliday - forthcoming - In Nicola Olivetti & Rineke Verbrugge (eds.), Advances in Modal Logic, Vol. 11. London: College Publications.
    Inquisitive logic is a research program seeking to expand the purview of logic beyond declarative sentences to include the logic of questions. To this end, inquisitive propositional logic extends classical propositional logic for declarative sentences with principles governing a new binary connective of inquisitive disjunction, which allows the formation of questions. Recently inquisitive logicians have considered what happens if the logic of declarative sentences is assumed to be intuitionistic rather than classical. In short, what should inquisitive logic be on an (...)
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  18. Possibility Semantics.Wesley H. Holliday - forthcoming - In Melvin Fitting (ed.), Selected Topics from Contemporary Logics. London: College Publications.
    In traditional semantics for classical logic and its extensions, such as modal logic, propositions are interpreted as subsets of a set, as in discrete duality, or as clopen sets of a Stone space, as in topological duality. A point in such a set can be viewed as a "possible world," with the key property of a world being primeness—a world makes a disjunction true only if it makes one of the disjuncts true—which classically implies totality—for each proposition, a world either (...)
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  19. Meta-Inferences and Supervaluationism.Luca Incurvati & Julian J. Schlöder - forthcoming - Journal of Philosophical Logic:1-34.
    Many classically valid meta-inferences fail in a standard supervaluationist framework. This allegedly prevents supervaluationism from offering an account of good deductive reasoning. We provide a proof system for supervaluationist logic which includes supervaluationistically acceptable versions of the classical meta-inferences. The proof system emerges naturally by thinking of truth as licensing assertion, falsity as licensing negative assertion and lack of truth-value as licensing rejection and weak assertion. Moreover, the proof system respects well-known criteria for the admissibility of inference rules. Thus, supervaluationists (...)
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  20. A Logic for Factive Ignorance.Ekaterina Kubyshkina & Mattia Petrolo - forthcoming - Synthese 198 (6):5917-5928.
    In the current debate there are two epistemological approaches to the definition of ignorance: the Standard View and the New View. The former defines ignorance simply as not knowing, while the latter defines it as the absence of true belief. One of the main differences between these two positions lies in rejecting (Standard View) or in accepting (New View) the factivity of ignorance, i.e., if an agent is ignorant of φ, then φ is true. In the present article, we first (...)
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  21. Modal Logics I: Modalities and Intensional Languages'.Ruth Bar Can Marcus - forthcoming - Boston Studies in the Philosophy of Science.
  22. Free Choice in Modal Inquisitive Logic.Karl Nygren - forthcoming - Journal of Philosophical Logic:1-45.
    This paper investigates inquisitive extensions of normal modal logic with an existential modal operator taken as primitive. The semantics of the existential modality is generalized to apply to questions, as well as statements. When the generalized existential modality is applied to a question, the result is a statement that roughly expresses that each way of resolving the question is consistent with the available information. I study the resulting logic both from a semantic and from a proof-theoretic point of view. I (...)
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  23. Dynamic Consequence for Soft Information.Olivier Roy & Ole Thomassen Hjortland - forthcoming - Journal of Logic and Computation.
  24. Existence and Modality in Kant: Lessons From Barcan.Andrew Stephenson - forthcoming - Philosophical Review.
    This essay considers Kant’s theory of modality in light of a debate in contemporary modal metaphysics and modal logic concerning the Barcan formulas. The comparison provides a new and fruitful perspective on Kant’s complex and sometimes confusing claims about possibility and necessity. Two central Kantian principles provide the starting point for the comparison: that the possible must be grounded in the actual and that existence is not a real predicate. Both are shown to be intimately connected to the Barcan formulas, (...)
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  25. Themes From Barcan Marcus.Timothy Williamson - forthcoming - Lauener Library of Analytical Philosophy, Vol. 3.
  26. A Theory of Necessities.Andrew Bacon & Jin Zeng - 2022 - Journal of Philosophical Logic 51 (1):151-199.
    We develop a theory of necessity operators within a version of higher-order logic that is neutral about how fine-grained reality is. The theory is axiomatized in terms of the primitive of *being a necessity*, and we show how the central notions in the philosophy of modality can be recovered from it. Various questions are formulated and settled within the framework, including questions about the ordering of necessities under strength, the existence of broadest necessities satisfying various logical conditions, and questions about (...)
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  27. A Philosophically Neutral Semantics for Perception Sentences.Samuele Iaquinto & Giuseppe Spolaore - 2022 - Theoria 88:532-544.
    Jaakko Hintikka proposed treating objectual perception sentences, such as “Alice sees Bob,” as de re propositional perception sentences. Esa Saarinen extended Hintikka’s idea to eventive perception sentences, such as “Alice sees Bob smile.” These approaches, elegant as they may be, are not philosophically neutral, for they presuppose, controversially, that the content of all perceptual experiences is propositional in nature. The aim of this paper is to propose a formal treatment of objectual and eventive perception sentences that builds on Hintikka’s modal (...)
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  28. A Puzzle About the Fixity of the Past.Fabio Lampert - 2022 - Analysis 82 (3):426-434.
    It is a widely held principle that no one is able to do something that would require the past to have been different from how it actually is. This principle of the fixity of the past has been presented in numerous ways, playing a crucial role in arguments for logical and theological fatalism, and for the incompatibility of causal determinism and the ability to do otherwise. I will argue that, assuming bivalence, this principle is in conflict with standard views about (...)
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  29. The Logic of Sequence Frames.Fabio Lampert - 2022 - Review of Symbolic Logic 15 (1):101-132.
    This paper investigates and develops generalizations of two-dimensional modal logics to any finite dimension. These logics are natural extensions of multidimensional systems known from the literature on logics for a priori knowledge. We prove a completeness theorem for propositional n-dimensional modal logics and show them to be decidable by means of a systematic tableau construction.
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  30. Automating Reasoning with Standpoint Logic Via Nested Sequents.Tim Lyon & Lucía Gómez Álvarez - 2022 - In Proceedings of the 19th International Conference on Principles of Knowledge Representation and Reasoning. pp. 257-266.
    Standpoint logic is a recently proposed formalism in the context of knowledge integration, which advocates a multi-perspective approach permitting reasoning with a selection of diverse and possibly conflicting standpoints rather than forcing their unification. In this paper, we introduce nested sequent calculi for propositional standpoint logics---proof systems that manipulate trees whose nodes are multisets of formulae---and show how to automate standpoint reasoning by means of non-deterministic proof-search algorithms. To obtain worst-case complexity-optimal proof-search, we introduce a novel technique in the context (...)
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  31. Norms and Alternatives : Logical Aspects of Normative Reasoning.Karl Nygren - 2022 - Dissertation, Stockholm University
    In this thesis, I develop and investigate various novel semantic frameworks for deontic logic. Deontic logic concerns the logical aspects of normative reasoning. In particular, it concerns reasoning about what is required, allowed and forbidden. I focus on two main issues: free-choice reasoning and the role of norms in deontic logic. -/- Free-choice reasoning concerns permissions and obligations that offer choices between different actions. Such permissions and obligations are typically expressed by a disjunctive clause in the scope of a deontic (...)
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  32. Peirce and Łukasiewicz on Modal and Multi-Valued Logics.Jon Alan Schmidt - 2022 - Synthese 200 (4):1-18.
    Charles Peirce incorporates modality into his Existential Graphs by introducing the broken cut for possible falsity. Although it can be adapted to various modern modal logics, Zeman demonstrates that making no other changes results in a version that he calls Gamma-MR, an implementation of Jan Łukasiewicz's four-valued Ł-modal system. It disallows the assertion of necessity, reflecting a denial of determinism, and has theorems involving possibility that seem counterintuitive at first glance. However, the latter is a misconception that arises from overlooking (...)
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  33. A Henkin-Style Completeness Proof for the Modal Logic S5.Bruno Bentzen - 2021 - In Pietro Baroni, Christoph Benzmüller & Yì N. Wáng (eds.), Logic and Argumentation: Fourth International Conference, CLAR 2021, Hangzhou, China, October 20–22. Springer. pp. 459-467.
    This paper presents a recent formalization of a Henkin-style completeness proof for the propositional modal logic S5 using the Lean theorem prover. The proof formalized is close to that of Hughes and Cresswell, but the system, based on a different choice of axioms, is better described as a Mendelson system augmented with axiom schemes for K, T, S4, and B, and the necessitation rule as a rule of inference. The language has the false and implication as the only primitive logical (...)
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  34. Display to Labeled Proofs and Back Again for Tense Logics.Agata Ciabattoni, Tim Lyon, Revantha Ramanayake & Alwen Tiu - 2021 - ACM Transactions on Computational Logic 22 (3):1-31.
    We introduce translations between display calculus proofs and labeled calculus proofs in the context of tense logics. First, we show that every derivation in the display calculus for the minimal tense logic Kt extended with general path axioms can be effectively transformed into a derivation in the corresponding labeled calculus. Concerning the converse translation, we show that for Kt extended with path axioms, every derivation in the corresponding labeled calculus can be put into a special form that is translatable to (...)
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  35. Logics of Imprecise Comparative Probability.Yifeng Ding, Wesley H. Holliday & Thomas F. Icard - 2021 - International Journal of Approximate Reasoning 132:154-180.
    This paper studies connections between two alternatives to the standard probability calculus for representing and reasoning about uncertainty: imprecise probability andcomparative probability. The goal is to identify complete logics for reasoning about uncertainty in a comparative probabilistic language whose semantics is given in terms of imprecise probability. Comparative probability operators are interpreted as quantifying over a set of probability measures. Modal and dynamic operators are added for reasoning about epistemic possibility and updating sets of probability measures.
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  36. The Bounds of Possibility: Puzzles of Modal Variation.Cian Dorr, John Hawthorne & Juhani Yli-Vakkuri - 2021 - Oxford: Oxford University Press.
    In general, a given object could have been different in certain respects. For example, the Great Pyramid could have been somewhat shorter or taller; the Mona Lisa could have had a somewhat different pattern of colours; an ordinary table could have been made of a somewhat different quantity of wood. But there seem to be limits. It would be odd to suppose that the Great Pyramid could have been thimble-sized; that the Mona Lisa could have had the pattern of colours (...)
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  37. An impossibility result on methodological individualism.Hein Duijf, Allard Tamminga & Frederik Van De Putte - 2021 - Philosophical Studies 178 (12):4165-4185.
    Methodological individualists often claim that any social phenomenon can ultimately be explained in terms of the actions and interactions of individuals. Any Nagelian version of methodological individualism requires that there be bridge laws that translate social statements into individualistic ones. We show that Nagelian individualism can be put to logical scrutiny by making the relevant social and individualistic languages fully explicit and mathematically precise. In particular, we prove that the social statement that a group of agents performs a deontically admissible (...)
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  38. Life and Actuality: On Placing Possibility in Hegel's Modal Metaphysics.Ekin Erkan - 2021 - Cosmos and History 17 (3):171-195.
    This paper looks at dialectical inferences as they relate to Hegel’s modal metaphysics, closely examining the Actuality section of Hegel’s Science of Logic and positing a reading of Hegel’s modal actualism that engages with two strains of secondary commentary. Responding to commentators, we make the case that Hegel’s ‘das Logische’ avoids presupposing possibility’s being prior to actuality insofar as actuality and the derivation of possibility is considered as the in-itselfness of actuality, an implicit inner moment whereby actuality further determines itself. (...)
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  39. Lógica modal megárico-estoica: posibilidad y necesidad como operadores atléticos.José Alejandro Fernández Cuesta - 2021 - Human Review. International Humanities Review / Revista Internacional de Humanidades 10:261-270.
    En este artículo presentamos una posible vía para interpretar las nociones de posibilidad y necesidad desarrolladas en el seno de la lógica megárico-estoica como operadores modales aléticos. Se introducirá la semántica megárico-estoica como trasfondo metafísico de las definiciones de necesidad y posibilidad y se ofrecerán argumentos para abandonar las interpretaciones predominantes que incluyen variables temporales ad hoc. Tras proponer la lectura de las definiciones diodóricas desde una semántica modal relacional se señalará una serie de temas que merecen ser revisitados desde (...)
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  40. Alternative Semantics for Normative Reasoning with an Application to Regret and Responsibility.Daniela Glavaničová & Matteo Pascucci - 2021 - Logic and Logical Philosophy 30 (4):653-679.
    We provide a fine-grained analysis of notions of regret and responsibility (such as agent-regret and individual responsibility) in terms of a language of multimodal logic. This language undergoes a detailed semantic analysis via two sorts of models: (i) relating models, which are equipped with a relation of propositional pertinence, and (ii) synonymy models, which are equipped with a relation of propositional synonymy. We specify a class of strictly relating models and show that each synonymy model can be transformed into an (...)
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  41. One-Step Modal Logics, Intuitionistic and Classical, Part 1.Harold T. Hodes - 2021 - Journal of Philosophical Logic 50 (5):837-872.
    This paper and its sequel “look under the hood” of the usual sorts of proof-theoretic systems for certain well-known intuitionistic and classical propositional modal logics. Section 1 is preliminary. Of most importance: a marked formula will be the result of prefixing a formula in a propositional modal language with a step-marker, for this paper either 0 or 1. Think of 1 as indicating the taking of “one step away from 0.” Deductions will be constructed using marked formulas. Section 2 presents (...)
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  42. Modeling Legal Conflict Resolution Based on Dynamic Logic.Fengkui Ju, Karl Nygren & Tianwen Xu - 2021 - Journal of Logic and Computation 31 (4):1102-1128.
    Conflicts between legal norms are common in reality. In many legislations, legal conflicts between norms are resolved by applying ordered principles. This work presents a formalization of the conflict resolution mechanism and introduces action legal logic (⁠ALL) to reason about the normative consequences of possibly conflicting legal systems. The semantics of ALL is explicitly based on legal systems consisting of norms and ordered principles. Legal systems specify the legal status of transitions in transition systems and the language of ALL describes (...)
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  43. Can Hardcore Actualism Validate S5?Samuel Kimpton-Nye - 2021 - Philosophy and Phenomenological Research 102 (2):342-358.
    Hardcore actualism (HA) grounds all modal truths in the concrete constituents of the actual world (see, e.g., Borghini and Williams (2008), Jacobs (2010), Vetter (2015)). I bolster HA, and elucidate the very nature of possibility (and necessity) according to HA, by considering if it can validate S5 modal logic. Interestingly, different considerations pull in different directions on this issue. To resolve the tension, we are forced to think hard about the nature of the hardcore actualist's modal reality and how radically (...)
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  44. Nested Sequents for Intuitionistic Modal Logics Via Structural Refinement.Tim Lyon - 2021 - In Anupam Das & Sara Negri (eds.), Automated Reasoning with Analytic Tableaux and Related Methods: TABLEAUX 2021. 93413 Cham, Germany: pp. 409-427.
    We employ a recently developed methodology -- called "structural refinement" -- to extract nested sequent systems for a sizable class of intuitionistic modal logics from their respective labelled sequent systems. This method can be seen as a means by which labelled sequent systems can be transformed into nested sequent systems through the introduction of propagation rules and the elimination of structural rules, followed by a notational translation. The nested systems we obtain incorporate propagation rules that are parameterized with formal grammars, (...)
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  45. Refining Labelled Systems for Modal and Constructive Logics with Applications.Tim Lyon - 2021 - Dissertation, Technischen Universität Wien
    This thesis introduces the "method of structural refinement", which serves as a means of transforming the relational semantics of a modal and/or constructive logic into an 'economical' proof system by connecting two proof-theoretic paradigms: labelled and nested sequent calculi. The formalism of labelled sequents has been successful in that cut-free calculi in possession of desirable proof-theoretic properties can be automatically generated for large classes of logics. Despite these qualities, labelled systems make use of a complicated syntax that explicitly incorporates the (...)
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  46. A Framework for Intuitionistic Grammar Logics.Tim Lyon - 2021 - In Pietro Baroni, Christoph Benzmüller & Yὶ N. Wang (eds.), Lecture Notes in Computer Science. 93413 Cham, Germany: pp. 495-503.
    We generalize intuitionistic tense logics to the multi-modal case by placing grammar logics on an intuitionistic footing. We provide axiomatizations for a class of base intuitionistic grammar logics as well as provide axiomatizations for extensions with combinations of seriality axioms and what we call "intuitionistic path axioms". We show that each axiomatization is sound and complete with completeness being shown via a typical canonical model construction.
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  47. Deontic Logic Based on Inquisitive Semantics.Karl Nygren - 2021 - In Fenrong Liu, Alessandra Marra, Paul Portner & Frederik Van De Putte (eds.), Deontic Logic and Normative Systems: 15th International Conference, DEON 2020/2021. London: College Publications. pp. 339-357.
    This paper introduces deontic logic based on inquisitive semantics. A semantics for action formulas is introduced where each action formula is associated with a set of alternatives. Deontic operators are then interpreted as quantifying over all alternatives associated with the action formulas within their scope. It is shown how this construction provides solutions to problems related to free choice permissions and obligations, including issues concerning Hurford disjunctions. The main technical result is a complete axiomatization of the logic.
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  48. An Incompleteness Theorem for Modal Relevant Logics.Shawn Standefer - 2021 - Notre Dame Journal of Formal Logic 62 (4):669 - 681.
    In this paper, an incompleteness theorem for modal extensions of relevant logics is proved. The proof uses elementary methods and builds upon the work of Fuhrmann.
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  49. Non-Boolean Classical Relevant Logics II: Classicality Through Truth-Constants.Tore Fjetland Øgaard - 2021 - Synthese (3-4):1-33.
    This paper gives an account of Anderson and Belnap’s selection criteria for an adequate theory of entailment. The criteria are grouped into three categories: criteria pertaining to modality, those pertaining to relevance, and those related to expressive strength. The leitmotif of both this paper and its prequel is the relevant legitimacy of disjunctive syllogism. Relevant logics are commonly held to be paraconsistent logics. It is shown in this paper, however, that both E and R can be extended to explosive logics (...)
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  50. The Barcan Formulas and Necessary Existence: The View From Quarc.Hanoch Ben-Yami - 2020 - Synthese 198 (11):11029-11064.
    The Modal Predicate Calculus gives rise to issues surrounding the Barcan formulas, their converses, and necessary existence. I examine these issues by means of the Quantified Argument Calculus, a recently developed, powerful formal logic system. Quarc is closer in syntax and logical properties to Natural Language than is the Predicate Calculus, a fact that lends additional interest to this examination, as Quarc might offer a better representation of our modal concepts. The validity of the Barcan formulas and their converses is (...)
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