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Shramko [(2016). Truth, falsehood, information and beyond: The American plan generalized. In K. Bimbo (Ed.), J. Michael Dunn on information based logics, outstanding contributions to logic (pp. 191–212). Dordrecht: Springer] formulated multilattice logic and the algebraic completeness theorem for it. However, the proof has not been presented. In this paper, we consider Kamide and Shramko's multilattice logic M L n [Kamide & Shramko (2017a). Embedding from multilattice logic into classical logic and vice versa. Journal of Logic and Computation, 27(5), 1549–1575] which is an extension of Shramko's original multilattice logic by several implications and coimplications. Using the technique of algebraic embedding, we show that Kamide and Shramko's sequent calculus for multilattice logic M L n is sound and complete with respect to multilattices. Moreover, we introduce yet another algebraic semantics for this logic based on the notion of a De Morgan multilattice. Using Lindenbaum-Tarski algebras, we show that M L n is sound and complete with respect to De Morgan multilattices. Besides, we modify Kamide and Shramko's notion of modal multilattice [Kamide & Shramko (2017b). Modal multilattice logic. Logica Universalis, 11(3), 317–343], i.e. we present the concept of De Morgan modal multilattice. We prove that Kamide and Shramko's modal multilattice logic (Kamide & Shramko, 2017b) is adequate with respect to De Morgan modal multilattices. [ABSTRACT FROM AUTHOR]

In the paper, we introduce multilattice versions of the basic congruent and monotonic modal logics. In the case of congruent and monotonic ones, we also study their extensions by Gödel's rule. We formulate these logics in the form of sequent calculi and prove syntactic embedding theorems (as a consequence, we obtain cut admissibility and decidability). Then we present them algebraically and semantically: via modal multilattices and via general and descriptive neighbourhood frames. We show the dual equivalency of the categories of modal multilattices and descriptive neighbourhood frames. Using Lindenbaum–Tarski algebras, we prove that the sequent calculi under consideration are sound and complete with respect to modal multilattices. [ABSTRACT FROM AUTHOR]

In Pietroski (2018) a simple representation language called SMPL is introduced, construed as a hypothesis about core conceptual structure. The present work is a study of this system from a logical perspective. In addition to establishing a completeness result and a complexity characterization for reasoning in the system, we also pinpoint its expressive limits, in particular showing that the fourth corner in the square of opposition ("Some_not") eludes expression. We then study a seemingly small extension, called SMPL+, which allows for a minimal predicate-binding operator. Perhaps surprisingly, the resulting system is shown to encode precisely the concepts expressible in first-order logic. However, unlike the latter class, the class of SMPL+ expressions admits a simple procedural (context-free) characterization. Our contribution brings together research strands in logic—including natural logic, modal logic, description logic, and hybrid logic—with recent advances in semantics and philosophy of language. [ABSTRACT FROM AUTHOR]

A tree natural deduction system for Anderson and Belnap's relevant logic E is presented and shown equivalent to a Hilbertstyle axiomatization of E. Using an idea from Prawitz, a variant tree system is motivated and shown equivalent to the Hilbertstyle system via a detour through Anderson and Belnap's Fitch system for E. [ABSTRACT FROM AUTHOR]

There is a relatively recent trend in treating negation as a modal operator. One such reason is that doing so provides a uniform semantics for the negations of a wide variety of logics and arguably speaks to a longstanding challenge of Quine put to non-classical logics. One might be tempted to draw the conclusion that negation is a modal operator, a claim Francesco Berto (Mind, 124(495), 761-793, 2015) defends at length in a recent paper. According to one such modal account, the negation of a sentence is true at a world x just in case all the worlds at which the sentence is true are incompatible with x. Incompatibility is taken to be the key notion in the account, and what minimal properties a negation has comes down to which minimal conditions incompatibility satisfies. Our aims in this paper are twofold. First, we wish to point out problems for the modal account that make us question its tenability on a fundamental level. Second, in its place we propose an alternative, non-modal, account of negation as a contradictory-forming operator that we argue is superior to, and more natural than, the modal account. [ABSTRACT FROM AUTHOR]

We give a definition of bisimulation for conditional modalities interpreted on selection functions and prove the correspondence between bisimilarity and modal equivalence, generalizing the Hennessy–Milner Theorem to a wide class of conditional operators. We further investigate the operators and semantics to which these results apply. First, we show how to derive a solid notion of bisimulation for conditional belief, behaving as desired both on plausibility models and on evidence models. These novel definitions of bisimulations are exploited in a series of undefinability results. Second, we treat relativized common knowledge, underlining how the same results still hold for a different modality in a different semantics. Third, we show the flexibility of the approach by generalizing it to multi-agent systems, encompassing the case of multi-agent plausibility models. [ABSTRACT FROM AUTHOR]

In this introduction to the special issue '40 years of FDE', we offer an overview of the field and put the papers included in the special issue into perspective. More specifically, we first present various semantics and proof systems for FDE, and then survey some expansions of FDE by adding various operators starting with constants. We then turn to unary and binary connectives, which are classified in a systematic manner (affirmative/negative, extensional/intensional). First-order FDE is also briefly revisited, and we conclude by listing some open problems for future research. [ABSTRACT FROM AUTHOR]

A notorious difficulty with modal extensions over a non-distributive propositional basis is to construct canonical Kripke models (time flow structures, when a temporal interpretation is intended) that respect the well-established intuitions about the meaning of modal (temporal) operators. Indeed, advances in modal logics over a non-distributive propositional basis over the last decade or so address a number of issues of significance, such as Sahlqvist (algorithmic) correspondence and completeness, yet they do this while resting on a notion of frame and model, canonical or otherwise, that compromises the intuitive semantics of the modal operators in important ways. This becomes particularly apparent when a dynamic, or a temporal reading of boxes and diamonds is intended. This article is restricted to the simplest temporal logic, a Priorean Tense Logic over a negation and implication free non-distributive propositional basis. We build up to this system by considering separately systems with modal operators in isolation, or in related groups, and we prove, for each system, completeness via a traditional canonicity argument. We establish that the absence of a distributivity assumption of conjunctions over disjunctions and conversely has no effect on the interpretation of boxes and diamonds, which are interpreted exactly as in classical normal modal logics. The motivation of this work resides in the realization that at least part of the reason for the manifest dissatisfaction with studying and applying modal logics over a non-distributive propositional basis is due precisely to the fact that a large number of semantic intuitions, results and techniques familiar from distributive logics seem to have to be inescapably abandoned. We argue in this article that this is not necessarily the case. The results we present can be applied, e.g. in studying dynamic, or temporal extensions of Orthomodular Quantum Logic, as well as in the relational semantics for Substructural Logics. [ABSTRACT FROM AUTHOR]

One of the most dominant approaches to semantics for relevant (and many paraconsistent) logics is the Routley-Meyer semantics involving a ternary relation on points. To some (many?), this ternary relation has seemed like a technical trick devoid of an intuitively appealing philosophical story that connects it up with conditionality in general. In this paper, we respond to this worry by providing three different philosophical accounts of the ternary relation that correspond to three conceptions of conditionality. We close by briefly discussing a general conception of conditionality that may unify the three given conceptions. [ABSTRACT FROM AUTHOR]

A new (sound and complete) proof style adequate for modal logics is defined from the polynomial ring calculus (PRC). The new semantics not only expresses truth conditions of modal formulas by means of polynomials, but also permits to perform deductions through polynomial handling. This paper also investigates relationships among the PRC here defined, the algebraic semantics for modal logics, equational logics, the Dijkstra–Scholten equational-proof style, and rewriting systems. The method proposed is throughly exemplified for S5, and can be easily extended to other modal logics. [ABSTRACT FROM AUTHOR]