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  1. Paraconsistent Metatheory: New Proofs with Old Tools.Guillermo Badia, Zach Weber & Patrick Girard - 2022 - Journal of Philosophical Logic 51 (4):825-856.
    This paper is a step toward showing what is achievable using non-classical metatheory—particularly, a substructural paraconsistent framework. What standard results, or analogues thereof, from the classical metatheory of first order logic can be obtained? We reconstruct some of the originals proofs for Completeness, Löwenheim-Skolem and Compactness theorems in the context of a substructural logic with the naive comprehension schema. The main result is that paraconsistent metatheory can ‘re-capture’ versions of standard theorems, given suitable restrictions and background assumptions; but the shift (...)
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  • Proofs and Models in Naive Property Theory: A Response to Hartry Field's ‘Properties, Propositions and Conditionals’.Greg Restall, Rohan French & Shawn Standefer - 2020 - Australasian Philosophical Review 4 (2):162-177.
    ABSTRACT In our response Field's ‘Properties, Propositions and Conditionals’, we explore the methodology of Field's program. We begin by contrasting it with a proof-theoretic approach and then commenting on some of the particular choices made in the development of Field's theory. Then, we look at issues of property identity in connection with different notions of equivalence. We close with some comments relating our discussion to Field's response to Restall’s [2010] ‘What Are We to Accept, and What Are We to Reject, (...)
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  • Ultralogic as Universal?: The Sylvan Jungle - Volume 4.Richard Routley - 2019 - Cham, Switzerland: Springer Verlag.
    Ultralogic as Universal? is a seminal text in non-classcial logic. Richard Routley presents a hugely ambitious program: to use an 'ultramodal' logic as a universal key, which opens, if rightly operated, all locks. It provides a canon for reasoning in every situation, including illogical, inconsistent and paradoxical ones, realized or not, possible or not. A universal logic, Routley argues, enables us to go where no other logic—especially not classical logic—can. Routley provides an expansive and singular vision of how a universal (...)
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  • Modal Logic Without Contraction in a Metatheory Without Contraction.Patrick Girard & Zach Weber - 2019 - Review of Symbolic Logic 12 (4):685-701.
    Standard reasoning about Kripke semantics for modal logic is almost always based on a background framework of classical logic. Can proofs for familiar definability theorems be carried out using anonclassical substructural logicas the metatheory? This article presents a semantics for positive substructural modal logic and studies the connection between frame conditions and formulas, via definability theorems. The novelty is that all the proofs are carried out with anoncontractive logicin the background. This sheds light on which modal principles are invariant under (...)
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  • Non-Classical Circular Definitions.Shawn Standefer - 2017 - Australasian Journal of Logic 14 (1).
    Circular denitions have primarily been studied in revision theory in the classical scheme. I present systems of circular denitions in the Strong Kleene and supervaluation schemes and provide complete proof systems for them. One class of denitions, the intrinsic denitions, naturally arises in both schemes. I survey some of the features of this class of denitions.
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  • Truth, Pretense and the Liar Paradox.Bradley Armour-Garb & James A. Woodbridge - 2015 - In T. Achourioti, H. Galinon, J. Martínez Fernández & K. Fujimoto (eds.), Unifying the Philosophy of Truth. Dordrecht: Imprint: Springer. pp. 339-354.
    In this paper we explain our pretense account of truth-talk and apply it in a diagnosis and treatment of the Liar Paradox. We begin by assuming that some form of deflationism is the correct approach to the topic of truth. We then briefly motivate the idea that all T-deflationists should endorse a fictionalist view of truth-talk, and, after distinguishing pretense-involving fictionalism (PIF) from error- theoretic fictionalism (ETF), explain the merits of the former over the latter. After presenting the basic framework (...)
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  • Analytic Calculi for Circular Concepts by Finite Revision.Riccardo Bruni - 2013 - Studia Logica 101 (5):915-932.
    The paper introduces Hilbert– and Gentzen-style calculi which correspond to systems ${\mathsf{C}_{n}}$ from Gupta and Belnap [3]. Systems ${\mathsf{C}_{n}}$ were shown to be sound and complete with respect to the semantics of finite revision. Here, it is shown that Gentzen-style systems ${\mathsf{GC}_{n}}$ admit a syntactic proof of cut elimination. As a consequence, it follows that they are consistent.
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  • Prospects for a Naive Theory of Classes.Hartry Field, Harvey Lederman & Tore Fjetland Øgaard - 2017 - Notre Dame Journal of Formal Logic 58 (4):461-506.
    The naive theory of properties states that for every condition there is a property instantiated by exactly the things which satisfy that condition. The naive theory of properties is inconsistent in classical logic, but there are many ways to obtain consistent naive theories of properties in nonclassical logics. The naive theory of classes adds to the naive theory of properties an extensionality rule or axiom, which states roughly that if two classes have exactly the same members, they are identical. In (...)
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  • On contraction and the modal fragment.Kai Brünnler, Dieter Probst & Thomas Studer - 2008 - Mathematical Logic Quarterly 54 (4):345-349.
    We observe that removing contraction from a standard sequent calculus for first-order predicate logic preserves completeness for the modal fragment.
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  • Uniform inseparability in explicit mathematics.Andrea Cantini & Pierluigi Minari - 1999 - Journal of Symbolic Logic 64 (1):313-326.
    We deal with ontological problems concerning basic systems of explicit mathematics, as formalized in Jäger's language of types and names. We prove a generalized inseparability lemma, which implies a form of Rice's theorem for types and a refutation of the strong power type axiom POW + . Next, we show that POW + can already be refuted on the basis of a weak uniform comprehension without complementation, and we present suitable optimal refinements of the remaining results within the weaker theory.
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  • Dialetheism and the countermodel problem.Andreas Fjellstad & Ben Martin - forthcoming - Philosophy and Phenomenological Research.
    According to some dialetheists, we ought to reject the distinction between object and meta‐languages. Given that dialetheists advocate truth‐value gluts within their object‐language, whether in order to solve the liar paradox or for some other reason, this rejection of the object‐/meta‐language distinction comes with the commitment to use a glutty metatheory. While it has been pointed out that a glutty metatheory brings with it expressive deficiencies, we highlight here another complication arising from the use of a glutty metatheory, this time (...)
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  • Property Identity and Relevant Conditionals.Zach Weber - 2020 - Australasian Philosophical Review 4 (2):147-155.
    ABSTRACT In ‘Properties, Propositions, and Conditionals’ Field [2021] advances further on our understanding of the logic and meaning of naive theories – theories that maintain, in the face of paradox, basic assumptions about properties and propositions. His work follows in a tradition going back over 40 years now, of using Kripke fixed-point model constructions to show how naive schemas can be (Post) consistent, as long as one embeds in a non-classical logic. A main issue in all this research is the (...)
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  • On closure and truth in substructural theories of truth.Zach Weber - 2016 - Synthese 199 (Suppl 3):725-739.
    Closure is the idea that what is true about a theory of truth should be true in it. Commitment to closure under truth motivates non-classical logic; commitment to closure under validity leads to substructural logic. These moves can be thought of as responses to revenge problems. With a focus on truth in mathematics, I will consider whether a noncontractive approach faces a similar revenge problem with respect to closure under provability, and argue that if a noncontractive theory is to be (...)
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  • On the crispness of and arithmetic with a bisimulation in a constructive naive set theory.S. Yatabe - 2014 - Logic Journal of the IGPL 22 (3):482-493.
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  • Light affine set theory: A naive set theory of polynomial time.Kazushige Terui - 2004 - Studia Logica 77 (1):9 - 40.
    In [7], a naive set theory is introduced based on a polynomial time logical system, Light Linear Logic (LLL). Although it is reasonably claimed that the set theory inherits the intrinsically polytime character from the underlying logic LLL, the discussion there is largely informal, and a formal justification of the claim is not provided sufficiently. Moreover, the syntax is quite complicated in that it is based on a non-traditional hybrid sequent calculus which is required for formulating LLL.In this paper, we (...)
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  • (1 other version)Systems for Non-Reflexive Consequence.Carlo Nicolai & Lorenzo Rossi - 2023 - Studia Logica 111 (6):947-977.
    Substructural logics and their application to logical and semantic paradoxes have been extensively studied. In the paper, we study theories of naïve consequence and truth based on a non-reflexive logic. We start by investigating the semantics and the proof-theory of a system based on schematic rules for object-linguistic consequence. We then develop a fully compositional theory of truth and consequence in our non-reflexive framework.
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  • Distinguishing non-standard natural numbers in a set theory within Łukasiewicz logic.Shunsuke Yatabe - 2007 - Archive for Mathematical Logic 46 (3-4):281-287.
    In ${\mathbf{H}}$ , a set theory with the comprehension principle within Łukasiewicz infinite-valued predicate logic, we prove that a statement which can be interpreted as “there is an infinite descending sequence of initial segments of ω” is truth value 1 in any model of ${\mathbf{H}}$ , and we prove an analogy of Hájek’s theorem with a very simple procedure.
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  • Observations on the Trivial World.Zach Weber & Hitoshi Omori - 2019 - Erkenntnis 84 (5):975-994.
    A world is trivial if it makes every proposition true all at once. Such a world is impossible, an absurdity. Our world, we hope, is not an absurdity. It is important, nevertheless, for semantic and metaphysical theories that we be able to reason cogently about absurdities—if only to see that they are absurd. In this note we describe methods for ‘observing’ absurd objects like the trivial world without falling in to incoherence, using some basic techniques from modal logic. The goal (...)
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  • Comprehension contradicts to the induction within Łukasiewicz predicate logic.Shunsuke Yatabe - 2009 - Archive for Mathematical Logic 48 (3-4):265-268.
    We introduce the simpler and shorter proof of Hajek’s theorem that the mathematical induction on ω implies a contradiction in the set theory with the comprehension principle within Łukasiewicz predicate logic Ł ${\forall}$ (Hajek Arch Math Logic 44(6):763–782, 2005) by extending the proof in (Yatabe Arch Math Logic, accepted) so as to be effective in any linearly ordered MV-algebra.
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  • On arithmetic in the Cantor- Łukasiewicz fuzzy set theory.Petr Hájek - 2005 - Archive for Mathematical Logic 44 (6):763-782.
    Axiomatic set theory with full comprehension is known to be consistent in Łukasiewicz fuzzy predicate logic. But we cannot assume the existence of natural numbers satisfying a simple schema of induction; this extension is shown to be inconsistent.
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  • On equality and natural numbers in Cantor-Lukasiewicz set theory.P. Hajek - 2013 - Logic Journal of the IGPL 21 (1):91-100.
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