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Summary

In classical logic, every sentence is entailed by a contradiction: A and ¬A together entail B, for any sentences A and B whatsoever. This principle is often known as ex contradictione sequitur quodlibet (from a contradiction, everything follows), or the explosion principle. In paraconsistent logic, by contrast, this principle does not hold: arbitrary contradictions do not paraconsistently entail every sentence. Accordingly, paraconsistent logics are said to be contradiction tolerant. Semantics for paraconsistent logics can be given in a number of ways, but a common theme is that a sentence is allowed to be both true and false simultaneously. This can be achieved by introducing a third truth-value, thought of as both true and false; alternatively, it can be achieved (in the propositional case) be replacing the usual valuation function with a relation between sentences and the usual truth-values, true and false, so that a sentence may be related to either or both of these. Those who think there really are true contradictions are dialethists. Not all paraconsistent logicians are dialethists: some present paraconsistent logic as a better notion of what follows from what, or as a way to reason about inconsistent data.

Key works Asenjo 1966 and da Costa 1974 develop the Logic of Paradox (based on theor earlier work on paraconsistency in the 1950s)Priest et al 1989 is a classic early collection of papers. Priest 2006 is the classic philosophical defense of paraconsistent logic (and of dialethism). 
Introductions da Costa & Bueno 2009 and Priest 2008 are good encyclopaedia entries on paraconsistent logic. The introduction to Priest 2006 is a clear statement of the case for paraconsistent logics; chapter 7 of Priest 2001 gives basic logical details of a few paraconsistent logics.
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  1. (1 other version)Paradoxes of Logical Equivalence and Identity.Andrew Bacon - 2013 - Topoi 1:1-10.
    In this paper a principle of substitutivity of logical equivalents salve veritate and a version of Leibniz’s law are formulated and each is shown to cause problems when combined with naive truth theories.
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  2. UPS Protocol Commentary: “= Is an Event” — σ One-Shot and Gate Discipline.Monstrosity C. - manuscript
    This paper systematizes the **UPS (Universal–Particular–Singular) Protocol** as an operational discipline in which **equality (`=`) is not a global property but a one-shot license event scoped to a window `W`**. The core points are: (i) **equality-as-event**, (ii) the **one-shot** character of the lag operator **σ**, (iii) passing the gate `Gate(W) = (stage = ????) ∧ δ_abs ∧ (σ_trace ≍) ∧ Guards(Exh/Det/Coh/No3/Arrow)`, (iv) **Non-Transport** across windows, and (v) **conservativity** of the `=`-free fragment over **FDE/LP**. On the report layer **D′** we operate (...)
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  3. UPS 프로토콜: 변증법의 운영적 형식화.Monstrosity C. - manuscript
    본 논문은 "변증법을 의미론이 아니라 운용 규율로 제시"한다. 우리는 U-P-S(Universal–Particular–Singular)라는 컨트롤 플레인과 B-T-Π(Values–Transitions–Propositions)라는 데이터 플레인을 정합적으로 접합하여, 모순(B)을 동력으로 보존하고 커밋(=) 으로만 결론을 승인하는 파이프라인을 제안한다. 등호는 전역 속성이 아니라 창 $W$ 범위의 단회 면허 사건이며(Non-Transport, No-Promotion), 과정 연산자 $σ$는 OneShot 으로 제한된다. 관측-동치($≈_{obs}$)가 항상 우선하며 전역 $π$는 금지된다. 의미론적으로는 Belnap/FDE 4값({$T, F, B, N$}, 지정값={$T,B$})을 채택하고, $Gate(W) := stage=\mathcal S ∧ δ_abs ∧ σ_trace≍ ∧ Guards(Exh/Det/Coh/No3-Lock/Arrow ∧ ¬mark$)$로 정의된 게이트 통과만이 커밋을 유발한다. 이 구성에서 폭발(EFQ: $p,¬p ⊢ q$)은 미유도이고, (...)
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  4. UPS Protocol: An Operational Formalization of Dialectic.Monstrosity C. - manuscript
    This paper presents dialectic not as semantics but as an operational discipline. We couple a control plane **U–P–S (Universal–Particular–Singular)** with a data plane **B–T–Π (Values–Transitions–Propositions)** to form a coherent pipeline that preserves contradiction as an engine (**B**) and authorizes conclusions only by **commit (=)**. Equality is not a global property but a **one-shot license event** scoped to a window **W** (**Non-Transport**, **No-Promotion**). The process operator **σ** is restricted to **one-shot**. **Observation‑equivalence (≈_obs)** has priority and any global **π** (a "God’s‑eye" perspective) (...)
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  5. Subject Unicity and Self-Ascription: A Paraconsistent Formalization with σ-Lag / 주체의 자기귀속과 단일성: σ-시차와 파라일관 논리의 형식화.Monstrosity C. - manuscript
    We present a formal account of subjectivity without external foundations. Over an extended LP/FDE truth alphabet, we axiomatize a self-ascriptive relation R(x,x) and a Subject Unicity (SU) scheme. We separate the linguistic lag operator X from the intra-perspectival successor σ, redefine same-place equivalence (≈), and license the identity sign (=) only via explicit upgrade anchors at the fix layer (Augenblick). Under a no-third-channel guard that blocks explosion while preserving the contradiction value B, we prove that within each connected cover the (...)
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  6. On the philosophical motivations for the logics of formal consistency and inconsistency.Walter Carnielli & Rodrigues Abilio - manuscript
    We present a philosophical motivation for the logics of formal inconsistency, a family of paraconsistent logics whose distinctive feature is that of having resources for expressing the notion of consistency within the object language. We shall defend the view according to which logics of formal inconsistency are theories of logical consequence of normative and epistemic character. This approach not only allows us to make inferences in the presence of contradictions, but offers a philosophically acceptable account of paraconsistency.
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  7. (1 other version)The external version of a subclassical logic.Massimiliano Carrara & Michele Pra Baldi - manuscript
    A three-valued logic L is subclassical when it is defined by a single matrix having the classical two-element matrix as a subreduct. In this case, the language of L can be expanded with special unary connectives, called external operators. The resulting logic L^e is the external version of L, a notion originally introduced by D. Bochvar in 1938 with respect to his weak Kleene logic. In this paper we study the semantic properties of the external version of a three-valued subclassical (...)
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  8. Is this a contradiction in Mathematics? (The paradox and Foundation of Mathematics, first version).Farzad Didehvar - manuscript
    In [Is Classical Mathematics Appropriate for Theory of Computation?] we show there is a contradiction which in [“Fuzzy Time”, a solution of Unexpected Hanging Paradox (A Fuzzy interpretation of Quantum Mechanics), Philpapers 2019-04-13] we give a solution for that. This is the starting point for new Theories, Theory of Fuzzy Time Computation and Fuzzy Time –Particle interpretation of quantum Mechanics. A question is remained which was mentioned in [Two points and two questions, F.Didehvar, Philpapers, Researchgate, 2025]. Is this contradiction a (...)
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  9. The Structural Ground of Logic.Lucas Gage - manuscript
    The classical laws of logic—identity, non-contradiction, and excluded middle—are almost universally treated as primitive axioms: presupposed by every argument but grounded by none. This paper proposes a derivation. It argues that any coherent existence-ground must differentiate into two co-primordial, antithetical aspects: bounded structural content (here designated SP, or 1) and its unbounded contextual background (here designated IP, or 0). This binary is not a logical construction but the ontological precondition for any information to exist at all—the structure that logic subsequently (...)
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  10. Reinterpreting the universe-multiverse debate in light of inter-model inconsistency in set theory.Daniel Kuby - manuscript
    In this paper I apply the concept of _inter-Model Inconsistency in Set Theory_ (MIST), introduced by Carolin Antos (this volume), to select positions in the current universe-multiverse debate in philosophy of set theory: I reinterpret H. Woodin’s _Ultimate L_, J. D. Hamkins’ multiverse, S.-D. Friedman’s hyperuniverse and the algebraic multiverse as normative strategies to deal with the situation of de facto inconsistency toleration in set theory as described by MIST. In particular, my aim is to situate these positions on the (...)
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  11. Proof of the Non-Existence of Contradiction: Zero-Morphism Degeneration and Indeterminacy in Multilayered Reality.Yuya Saito - manuscript
    This paper redefines the principle of non-contradiction (¬(P ∧ ¬P)) in classical logic not merely as a formal convention of thought, but as a structural “non-instantiability” within the universal system. We present a rigorous proof across five distinct layers—the physical, classical set-theoretic, quantum, computational, and category-theoretic—demonstrating the mechanisms by which contradiction is systematically avoided or annihilated. We conclude that “contradiction” as a physical entity does not exist; rather, what is perceived as undecidability or inconsistency is a convergence toward “Indeterminacy,” a (...)
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  12. Inconsistency in empirical sciences.Luis Felipe Bartolo Alegre -
    This paper deals with a relatively recent trend in the history of analytic philosophy, philosophical logic, and theory of science: the philosophical study of the role of inconsistency in empirical science. This paper is divided in three sections that correspond to the three types of inconsistencies identified: (i) factual, occurring between theory and observations, (ii) external, occurring between two mutually contradictory theories, and (iii) internal, characterising theories that entail mutually contradictory statements.
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  13. Bohr's atomic model and paraconsistent logic.Pandora Hadzidaki -
    Bohr’s atomic model is one of the better known examples of empirically successful, albeit inconsistent, theoretical schemes in the history of physics. For this reason, many philosophers use this model to illustrate their position for the occurrence and the function of inconsistency in science. In this paper, I proceed to a critical comparison of the structure and the aims of Bohr’s research program – the starting point of which was the formulation of his model – with some of its contemporary (...)
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  14. Vita impossibile del signor Clark Costa.Michelangelo Antonioni - forthcoming - Cinema.
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  15. Cruz Costa e Herdeiros nos Idos de Sessenta.Paulo Arantes - forthcoming - Filosofia.
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  16. Logical argumentation by dynamic proof systems.Ofer Arieli & Christian Straßer - forthcoming - Theoretical Computer Science.
    In this paper we provide a proof theoretical investigation of logical argumentation, where arguments are represented by sequents, conflicts between arguments are represented by sequent elimination rules, and deductions are made by dynamic proof systems extending standard sequent calculi. The idea is to imitate argumentative movements in which certain claims are introduced or withdrawn in the presence of counter-claims. This is done by a dynamic evaluation of sequences of sequents, in which the latter are considered ‘derived’ or ‘not derived’ according (...)
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  17. Bilateral Labeled Sequent Calculi.Fabio De Martin Polo - forthcoming - Notre Dame Journal of Formal Logic.
    This paper investigates the proof theory of contra-classical logics, with a focus on Heinrich Wansing’s constructive connexive logic C. Drawing on Wansing’s semantic ‘bilateral’ framework – which characterizes connectives in terms of ‘support of truth’ and ‘support of falsity’ – we introduce a bilateral labeled sequent calculus incorporating specific ‘verification’ and ‘falsification’ rules. The resulting calculus is shown to exhibit key structural properties: all logical rules are height-preserving invertible, all structural rules are height-preserving admissible, and the cut rule is admissible. (...)
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  18. Nonuniform Substitutions Can’t Get you From Classical Logic to any Traditional Relevant or Quasi-Relevant Logic.Shay Allen Logan - forthcoming - Analysis.
    The paper demonstrates that you cannot land anywhere at all between the basic relevant logic B and the strongest traditional relevant logic R by restricting classical logic to the largest of its subsets that is invariant under any plausible class of nonuniform substitutions. Nor does it help to extend the upper limit to one of the quasi-relevant logics like RM3 or KR. This is a serious but not-quite-fatal blow to a tantalizing possibility raised by a body of recent work in (...)
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  19. The Logic of Exemplarity.Jakub Mácha - forthcoming - Law and Literature (online first):1-15.
    The topic of exemplarity has attracted considerable interest in philosophy, legal theory, literary studies and art recently. There is broad consensus that exemplary cases mediate between singular instances and general concepts or norms. The aim of this article is to provide an additional perspective on the logic of exemplarity. First, inspired by Jacques Derrida’s discussion of exemplarity, I shall argue that there is a kind of différance between (singular) examples and (general) exemplars. What an example exemplifies, the exemplarity of the (...)
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  20. Recapturing Structural Properties with a Consistency Operator.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 323-346.
    Some years ago Walter Carnielli and his colleagues developed a novel way of approaching paraconsistency. They introduced primitive operators to handle the notions of consistency and inconsistency, and so they created a whole new family of logical systems: the logics of formal inconsistency (LFI). In this paper we present a conceptual characterization of two of the LFI’s most important operators, the so-called consistency and inconsistency operators. Based on the relation between the meaning of logical constants and the structural properties of (...)
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  21. Logical Desiderata on Statistical Inference.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 117-138.
    It is common to refer to statistics as “the logic of science”. This note can be seen as an attempt to take the dictum seriously. To do so we ask which properties are desirable for a (formal) logic of statistical inference. The question is potentially as vast as science itself, so for the present occasion we set ourselves the modest aim of framing it in a way which, we hope, can be of interest both to logicians and to statisticians.
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  22. A Fascination for Reasoning.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 1-28.
    This chapter is an intellectual autobiography centered on a lifelong commitment to the study of reasoning as a formal, epistemic, and mathematical phenomenon. My early fascination with concrete mathematics and discrete problem solving gradually evolved into a systematic engagement with logic in its proof-theoretical, model-theoretical, semantic, and operational dimensions. Throughout my career, I have worked on the foundations and development of non-classical logics, with particular emphasis on paraconsistent, paracomplete, modal, and many-valued systems, as well as on their interaction with probability (...)
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  23. Possible-Translation Semantics from a Categorical Point of View.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 65-87.
    In this paper we consider, with a categorial approach, previous ideas and previous work of Walter Carnielli (learned by the authors directly from Walter’s talks at CLE-Unicamp) concerning possible translation semantics and remote algebrization. We show that if logic remotely protoalgebrizable—i.e. it has a conservative translation into a protoalgebraizable logic—then it is has a theorem or it is “non-implosive” (i.e. any formula that is a consequence of every non-empty set is a theorem). A similar result is proved for the existence (...)
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  24. Introduction.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 29-35.
    It takes a great deal of intellectual courage and a fair amount of talent for a researcher to venture himself in a such a variety of fields such as Walter Carnielli did—and still does—along his career. Throughout more than 50 years dedicated to academic work, Carnielli has made important contributions to logic, mathematics, and philosophy, not only through his research activities, but also through the many graduate students he has supervised, as well as other students and researchers whom he has (...)
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  25. An Approach to Inconsistency-Tolerant Reasoning About Probability Based on Łukasiewicz Logic.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 283-322.
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  26. Walter Carnielli on Reasoning, Paraconsistency, and Probability.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - Cham: Springer Nature Switzerland.
    This book is a collection of essays and research articles honoring Walter Carnielli and his work. It brings together contributions from renowned scholars from all over the world whose work draws on or is somehow related to the several important researches Carnielli has conducted throughout his career. It includes advanced work in paraconsistent and non-classical logics, computability, probability theory, philosophy of logic, and philosophy of science. Carnielli’s contributions to logic are widely acknowledged by the scientific community, and encompass very diverse (...)
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  27. Paraconsistent and Paracomplete Popperian Probabilities.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 139-159.
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  28. Decidability of Consequence in Logics via Reduction.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 423-451.
    We adopt consequence systems as a highly suitable framework for introducing logical (decision) problems such as the Consequence Problem, the Theoremhood Problem and the Consistency Problem. Reductions play a key role in the reflection and preservation of decidability and non decidability, respectively. We consider two levels of reduction: reduction between decision problems and between consequence systems. Then, we establish sufficient conditions for the existence of reductions between problems over the same consequence system as well as across different consequence systems. We (...)
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  29. On the Philosophy and Mathematics of Hybrid Partial Type Theory.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 37-63.
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  30. Dynamic Epistemic Logic with ASP Updates: Application to Conditional Planning.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 161-193.
    Dynamic Epistemic Logic (DEL) is a family of multimodal logics that has proved to be very successful for epistemic reasoning in planning tasks. In this logic, the agent’s knowledge is captured by modal epistemic operators whereas the system evolution is described in terms of (some subset of) dynamic logic modalities in which actions are usually represented as semantic objects called event models. In this paper, we study a variant of DEL, that we call DEL[ASP], where actions are syntactically described by (...)
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  31. On ℵ0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\aleph _0$$\end{document}-Categorical Biregular Rings.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 347-379.
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  32. Beyond Paraconsistency: A Plea for a Radical Breach with the Aristotelean Orthodoxy in Logic.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 525-554.
    It is suggested to radically break with the time-honored Aristotelean tradition of complete banishment of contradictions in science. In particular, it is argued that it is theoretically rational to believe not only that there exist interesting or important non-trivial negation inconsistent theories but also that there exist interesting or important non-trivial negation inconsistent logics.
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  33. The (In)Consistency of Consistency.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 381-405.
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  34. Bibliography of Walter Carnielli.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 587-604.
    Carnielli, W.A. and Pizzi, C. Modalities and Multimodalities. Springer, 2008.
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  35. The e-Value and the Full Bayesian Significance Test: Logical Properties and Philosophical Consequences.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 487-524.
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  36. Nicholas of Autrecourt and Paraconsistency.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 231-249.
    In this paper we discuss the extant writings of the French medieval thinker Nicholas of Autrecourt. We analyse his definition of contradiction, his discussion about the principle of non-contradiction, and his notion of valid inference. We argue that he did not accept the validity of ex falso sequitur quodlibet and can be considered a paraconsistentist in the present-day broad sense. Since Autrecourt is not well-known among contemporary logicians and philosophers, we also present some brief historical notes about his life and (...)
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  37. Self-extensionality in Four-Valued Paradefinite Logics.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 89-115.
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  38. My Views on My Friends and Their Contributions.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 555-585.
    This chapter offers a reflective and critical engagement with the contributions collected in this volume. It presents a personal and conceptual assessment of the ideas, methods, and results developed by friends and collaborators of the volume, highlighting points of convergence, divergence, and open problems. The discussion emphasizes the logical, philosophical, and methodological themes that run through the volume, situating the individual contributions within broader debates in contemporary logic. The chapter thus aims to combine intellectual appreciation with critical analysis, in the (...)
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  39. Restricted Swap Structures for C-Systems: An Algebraic and Categorical Approach.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 195-230.
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  40. Modality and Dyadic Contingency.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 407-421.
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  41. A Logic Not Exactly Adopted.Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues - 2026 - In Henrique Antunes, Alfredo Roque Freire & Abilio Rodrigues, Walter Carnielli on Reasoning, Paraconsistency, and Probability. Cham: Springer Nature Switzerland. pp. 251-282.
    The problems of adopting a logic have received significant recent attention. Less noted is the fact that, for almost all logicians, the logic they adopted and the formal system they take as corresponding to it do not match. This is well-known, and largely ignored. The present paper explores rather than ignores.
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  42. On the Thorny Question of Impossible Antecedents.Andrea Iacona - 2026 - Philosophical Quarterly 76.
    There are essentially three ways to treat conditionals with impossible antecedents in a formal framework that employs classical truth values: one can hold that such conditionals are all true, that they are all false, or that some are true while others are false. These three options will be examined under the background hypothesis that a conditional is true when its antecedent is incompatible with the negation of its consequent. It will be argued that the third option can be coherently developed (...)
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  43. A Hypersequent Calculus for Classical Contingencies.Gabriele Pulcini & Achille C. Varzi - 2026 - Journal of Philosophical Logic 55 (1).
    We present a hypersequent calculus that is sound and complete with respect to the truth-functionally contingent formulas of classical logic. We investigate its structural properties and provide a Gentzen-style cut-elimination procedure. The most notable feature of the calculus is that it jointly satisfies the subformula property and the property of _deductive purity_, to the effect that only contingent hypersequents occur in formal proofs. Moreover, since the negation of a contingent formula is also contingent, the calculus turns out to be _paraconsistent_, (...)
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  44. Explosion and Reasoning.Daniele Sgaravatti - 2026 - Episteme 23 (1):141-155.
    The paper responds to two recent versions of the argument against ex contradictione quodlibet (the principle that says that a contradiction entails any proposition, also known as ‘explosion’) based on the normative role of logic for reasoning. Both versions of the argument I am concerned with assume that a subject has defeasible reasons to believe any logical consequence of her beliefs. After showing this assumption to be more controversial than it might seem, I argue that even if it is true, (...)
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  45. There Is a Logical Negation: "Yes," "No," Both, Neither.Ryan Simonelli - 2026 - Australasian Journal of Logic 23 (1):55-78.
    Jc Beall argues that if FDE is logic proper, then there is no logical negation. This claim is largely based on the fact that, in standard proof systems for FDE, there are no stand-alone negation rules that suffice to capture the behavior of negation. In this paper, I show that by adopting a bilateral proof system for FDE, one can maintain that there is a logical negation, it is the very same logical negation that belongs to classical logic, and its (...)
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  46. Inference to the Best Contradiction?Sam Baron - 2025 - British Journal for the Philosophy of Science 76 (3):759-781.
    I argue that there is nothing about the structure of inference to the best explanation (IBE) that prevents it from establishing a contradiction in general, though there are some potential limitations on when it can be used for this purpose. Studying the relationship between IBE and contradictions is worthwhile for three reasons. First, it enhances our understanding of IBE. We see that, in many cases, IBE does not require explanations to be consistent, though there are some cases where consistency may (...)
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  47. Peut-on tester si le mouvement est inconsistant?Luis F. Bartolo Alegre - 2025 - In Jean-Pierre Schneider & Daniel Schulthess, Mouvement : Actes du XXXIXe Congrès de l'ASPLF. Genève: Droz. pp. 97-106.
    Priest's theory of motion is based on Leibniz's Continuity Condition (LCC), which states that any state that exists at each instant in a continuous set of moments also exists at its temporal limit. If we accept the CCL, a free-falling pen would have to be simultaneously in motion and at rest at the instant of change: the critical moment when it hits the ground, thus passing from the state of motion to that of rest. This seems to be a contradictory (...)
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  48. Can we test inconsistent empirical theories?Luis F. Bartolo Alegre - 2025 - Logic and Logical Philosophy 34 (4):501–45.
    Despite the logical possibility and alleged existence of inconsistent empirical theories, the problem of their testability remains largely unexplored. I develop a testability criterion which makes some of these theories testable, including some observationally inconsistent ones. However, they are not rejectable qua inconsistent by this criterion. These results, while opening the domain of scientific theories to inconsistent ones, challenge the prospects of dialetheism in the philosophy of science.
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  49. (1 other version)The Impossible Arises: Oscar Reutersvärd and his Contemporaries. [REVIEW]Ben Blumson - 2025 - Australasian Journal of Philosophy 103 (1):277-282.
    The Impossible Arises is an art history and philosophy of impossible pictures, focused especially on the contributions of Oscar Reutersvärd. The book draws on an archive of Reutersvärd’s letters an...
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  50. (1 other version)The External Version of a Subclassical Logic.Massimiliano Carrara & Michele Pra Baldi - 2025 - Review of Symbolic Logic 18 (4).
    A three-valued logic is subclassical when it is defined by a single matrix having the classical two-element matrix as a subreduct. In this case, the language of can be expanded with special unary connectives, called external operators. The resulting logic is called the external version of, a notion originally introduced by D. Bochvar in 1938 with respect to his weak Kleene logic. In this paper we study the semantic properties of the external version of a three-valued subclassical logic. We determine (...)
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