Many-Valued Logic

The article presents the chess composition as a logical art, with concrete examples. It began with Arabic mansuba, and later evolved to new-strategy designed by Italian Alberto Mari. The redefinition of mate (e.g. mate with a free field) or a theme to quasi-pseudo theme, opens the new space for combinations, and enables to connect it with other fields like computer science. The article was exhibited in Holland Park, W8 6LU, The Ice House between 18. Oct - 3. Nov. 2013.

This paper presents a unified theory of the truth conditions and probability of indicative conditionals and their compounds in a trivalent framework. The semantics validates a Reduction Theorem: any compound of conditionals is semantically equivalent to a simple conditional. This allows us to validate Stalnaker's Thesis in full generality and to use Adams's notion of $p$-validity as a criterion for valid inference. Finally, this gives us an elegant account of Bayesian update with indicative conditionals, establishing that despite differences in meaning, (...) it is tantamount to learning a material conditional. (shrink)

This paper extends a trivalent semantics for indicative conditionals to a language including the modal operators "might" and "must". Specifically, we combine Cooper's (1968) truth-functional, trivalent analysis of the conditional connective with Kratzer's (1986, 2012) idea that if-clauses restrict modal operators. By hard-wiring both trivalence and the restriction operation into the truth conditions of conditional-modal expressions, we obtain an attractive theory that yields plausible predictions for the interaction of conditionals and modals, explains the intuitive appeal of the Restrictor View and (...) avoids the typical problems of Kratzer-style accounts, especially regarding the probability of conditional-modal expressions. (shrink)

This paper explores an alternative non-relational semantics for modal logic, framing modal systems as "poly-logics"—intersections of simpler, foundational logics. Building on pioneering work by J. Kearns and subsequent developments, we demonstrate how established systems such as K series (K, K4, K5, K45), KD series (KD, KD4, KD5, KD45), KB series (KDB, KB, KB4, KB5, KB45) emerge as intersections of logics like KT, KTB, FN, TR, and their extensions. Utilizing Resolution Matrix Semantics (RMS), we establish soundness and completeness for key systems (...) with sketched proofs and introduce an innovative tableau-based proof procedure tailored to RMS. This approach not only unifies disparate modal frameworks but also yields efficient algorithmic tools for validity checking, offering fresh insights into the algebraic structure of modal deduction. Examples illustrate the method's efficacy, highlighting its advantages over traditional Kripke-style model checking. (shrink)

Human thinking does not proceed within a single logic. It stabilizes meaning at the intersection of multiple, partially incompatible logics while tolerating indeterminacy. This paper develops quantum-inspired polylogical systems - formal framework in which this cognitive fact becomes a principle of inference. Building on Resolution Matrix Semantics, indeterminate truth values are interpreted as semantic superpositions, and logical systems themselves form a space of interacting constraints. Inference is reconceived not as derivation within a fixed logic, but as the emergence of stable (...) semantic configurations through interference and suppression. Unlike conventional quantum AI, which accelerates classical reasoning, the proposed model alters the semantics of inference itself. Poly-Logic Quantum AI thus offers a structural model of human reasoning—one that explains coherence without certainty, context sensitivity without logic switching, and the emergence of new ideas without randomness. The result is a theory of artificial reasoning closer to human thinking than to calculation. (shrink)

Is logic empirical? Is logic to be found in the world? Or is logic rather a convention, a product of conventions, part of the many rules that regulate the language game? Answers fall in either camp. We like the linguistic answer. In this paper, we want to analyze how a linguistic community would tackle the problem of developing a logic and show how the linguistic conventions adopted by the community determine the properties of the local logic. Then show how to (...) move from a notion of logic that varies from community to community to a notion of logic that is in a sense universal. The framework is conventional up to a point: we have sentences, atomic and composite, the connectives are interpreted, values are computed, and the value of a composite sentence is a function of the values of its subsentences. Less conventional is the use of a plurality of truth values, and the sharp distinction we draw between sentences and statements, in the spirit of the distinction between proposition and judgment that one may find in proof theory. The linguistic community will face many choices. What are the good ones, the ones to avoid? Are there, in some sense, optimal choices? These are the kind of issues we are addressing. Where do we end up? With some kind of universal bivalent logic, ironically enough. We start from an arbitrarily large number of truth values, atomic sentences and connectives, construct a generic many-valued logic, recover more or less the usual results and issues, and in the end it all comes down to a positive bivalent logic with two connectives, `and' and `or', as if logic is nothing more than a mere accounting of possibilities. (shrink)

This paper connects truthmaker semantics with a trivalent interpretation of the indicative conditional. This merger substantially extends the scope of both approaches and has attractive philosophical implications. First, we can unify a realist and an informational interpretation of when a state verifies or accepts a sentence. Second, the framework recaptures central features of various analyses of conditionals: the material conditional analysis, Leitgeb's HYPE conditional, the Chrysippus test, and the Ramsey test.

This paper defines a precise sense in which the material conditional analysis (MCA) is a successful heuristic for deductive reasoning with a suppositional conditional, interpreted by means of trivalent semantics. Both accounts generate the same theorems and valid deductive inferences in a large fragment of the conditional language. However, the suppositional analysis gives a more attractive treatment of conditional negation and the probability of conditionals. Therefore, this paper inverts Williamson's claim that suppositional reasoning is a heuristic for valid reasoning with (...) conditionals (on his account, given by MCA). Similarly, the logic C2 of Stalnaker's possible-world semantics for conditionals is interpreted as approximating probability-preserving inference with suppositional conditionals. (shrink)

The paper explores applications of Kripke's theory of truth to semantics for anti-luck epistemology, that is, to subjunctive theories of knowledge. Subjunctive theories put forward modal or subjunctive conditions to rule out knowledge by mere luck as to be found in Gettier-style counterexamples to the analysis of knowledge as justified true belief. Because of the subjunctive nature of these conditions the resulting semantics turns out to be non-monotone, even if it is based on non-classical evaluation schemes such as strong Kleene (...) or FDE. This blocks the usual road to fixed-point results for Kripke's theory of truth within these semantics and consequently the paper is predominantly an exploration of fixed point results for Kripke's theory of truth within non-monotone semantics. Using the theory of quasi-inductive definitions we show that in case of the subjunctive theories of knowledge the so-called Kripke jump will have fixed points despite the non-monotonicity of the semantics: Kripke's theory of truth can be successfully applied in the framework of subjunctive theories of knowledge. (shrink)

In this article I define a strong conditional for classical sentential logic, and then extend it to three non-classical sentential logics. It is stronger than the material conditional and is not subject to the standard paradoxes of material implication, nor is it subject to some of the standard paradoxes of C. I. Lewis’s strict implication. My conditional has some counterintuitive consequences of its own, but I think its pros outweigh its cons. In any case, one can always augment one’s language (...) with more than one conditional, and it may be that no single conditional will satisfy all of our intuitions about how a conditional should behave. Finally, I suspect the strong conditional will be of more use for logic rather than the philosophy of language, and I will make no claim that the strong conditional is a good model for any particular use of the indicative conditional in English or other natural languages. Still, it would certainly be a nice bonus if some modified version of the strong conditional could serve as one. -/- I begin by exploring some of the disadvantages of the material conditional, the strict conditional, and some relevant conditionals. I proceed to define a strong conditional for classical sentential logic. I go on to adapt this account to Graham Priest’s Logic of Paradox, to S. C. Kleene’s logic K3, and then to J. Łukasiewicz’s logic Ł, a standard version of fuzzy logic. (shrink)

This paper is a contribution to graded model theory, in the context of mathematical fuzzy logic. We study characterizations of classes of graded structures in terms of the syntactic form of their first-order axiomatization. We focus on classes given by universal and universal-existential sentences. In particular, we prove two amalgamation results using the technique of diagrams in the setting of structures valued on a finite MTL-algebra, from which analogues of the Łoś–Tarski and the Chang–Łoś–Suszko preservation theorems follow.

Validity is usually taken to be a bivalent property: every inference is either valid or invalid, and never both. We argue for the controversial thesis that, if one endorses a many-valued semantics for the object language, then one likely has good reasons to also endorse a manyvalued notion of validity. We present several logical systems (based on Belnap’s algebra 4) whose notion of validity is non-bivalent: there are inferences that are both valid and invalid, and/or inferences that are neither valid (...) nor invalid. We show that, under natural assumptions, the validity of metainferences is also non-bivalent in many of these systems. Lastly, we claim that our framework has fruitful applications to philosophical issues, such as the link between logical consequence and the conditional, and the link between logic and metalogic. (shrink)

This article aims to dualize several results concerning various types (including possibly Cut-free and Identity-free systems) of canonical multiple-conclusion sequent calculi, i.e. Gentzen-style deduction systems for sequents, equipped with well-behaved forms of left and right introduction rules for logical expressions. In this opportunity, we focus on a different kind of calculi that we dub cocanonical, that is, Gentzen-style deduction systems for sequents, equipped with well-behaved forms of left and right elimination rules for logical expressions. These systems, simply put, have rules (...) that proceed from sequents featuring complex formulas to sequents featuring their component subformulas. Our main goals are to prove soundness and completeness results for the target systems’ consequence relations in terms of their characteristic 3- or 4-valued non-deterministic matrices. (shrink)

This paper shows how to transform explosive many-valued systems into paraconsistent logics. We investigate mainly the case of three-valued systems exhibiting how non-explosive three-valued logics can be obtained from them.

This chapter gives some elements of the history of trivalent logics and presents the key technical notions. We stress that Boole and Frege were aware of reasons to go beyond bivalence, in ways that influenced Łukasiewicz in particular. Then we put particular emphasis on the 1930s as a pivotal moment in the application of trivalence to a range of interconnected phenomena, such as probability and hypothetical reasoning, quantum indeterminacy, computability theory, and the semantic paradoxes. The chapter goes on to present (...) basic elements regarding the connection of trivalent logics to other logics, including intuitionistic logic, modal logics, fuzzy and many-valued logics, and finally to classical and non-classical logics more broadly. Along the way, we present basic systems of mixed consequence, and provide glimpses into the theory of ternary computation. (shrink)

The aim of this article is to discuss pure variable inclusion logics, that is, logical systems where valid entailments require that the propositional variables occurring in the conclusion are included among those appearing in the premises, or vice versa. We study the subsystems of Classical Logic satisfying these requirements and assess the extent to which it is possible to characterise them by means of a single logical matrix. In addition, we semantically describe both of these companions to Classical Logic in (...) terms of appropriate matrix bundles and as semilattice-based logics, showing that the notion of consequence in these logics can be interpreted in terms of truth (or non-falsity) and meaningfulness (or meaninglessness) preservation. Finally, we use Płonka sums of matrices to investigate the pure variable inclusion companions of an arbitrary finitary logic. -/- . (shrink)

We explore certain algebraic structures that naturally emerge within the framework of logics of synonymy, analytic containment, and hyperintensionality. In particular, we argue that Angell's logic AC, one of the earliest and most successful attempts to analyse the properties of logical constants with a topic-transformative character, can be better understood through a direct algebraic study of De Morgan bisemilattices. Inter alia, we study and compare the quasivarieties of De Morgan bisemilattices generated by certain finite algebras considered in the literature, viewed (...) as formalising different approaches to the validity of inferences among statements of synonymy. (shrink)

By and large, the conditional connective in three-valued logic has two different functions. First, by means of a deduction theorem, it can express a specific relation of logical consequence in the logical language itself. Second, it can represent natural language structures such as "if/then'' or "implies''. This chapter surveys both approaches, shows why none of them will typically end up with a three-valued material conditional, and elaborates on connections to probabilistic reasoning.

By and large, the conditional connective in three-valued logic has two different functions. First, by means of a deduction theorem, it can express a specific relation of logical consequence in the logical language itself. Second, it can represent natural language structures such as "if/then'" or "implies''. This chapter surveys both approaches, shows why none of them will typically end up with a three-valued material conditional, and elaborates on connections to probabilistic reasoning.

We provide non-deterministic semantics for some content inclusion logics standing between the first-degree entailment fragments of Parry's logic PAI and Angell's logic of analytic implication AC. Our semantics is inspired by two-address semantics developed following ideas introduced by Herzberger and Woodruff, suggesting to independently evaluate formulas on their alethic and topical status. Building on this, we explore the results of allowing negation to be non-deterministic on either of these independent aspects. For this purpose, we emulate the presence of truth-value gaps (...) and gluts by letting negation work non-deterministically on the alethic coordinate. At the same time, we emulate the presence of topic-transformed negated formulas by letting negation work non-deterministically on the topical coordinate. The outcome is a unifying framework for classical logic and a vast collection of non-classical systems that characterize them according to how negation and the set of designated values are defined. (shrink)

This paper examines a range of logical systems within the family of variable inclusion logics—also known as containment logics. We focus on those logics that restrict classically valid inferences to ones meeting specific variable inclusion constraints, hence called variable inclusion companions of classical logic. These constraints can be seen as enforcing varying degrees of relevance between premises and conclusions, placing these systems within the broader tradition of relevance logics. We review established companions of Classical Logic, including Weak Kleene logics (Bochvar, (...) 1938, Halldén, 1949), pure variable inclusion logics (Paoli et al., 2021), uniform Weak Kleene logics (Borzi and Zirattu, forth.), and their intersection—pure uniform logics. We then introduce two new systems named analytic and synthetic companions of Classical Logic. We characterize their consequence relations and interpret them, as their names suggest, as validating only analytic and synthetic inferences. Lastly, we argue that these systems more effectively address the irrelevance cases that motivated earlier proposals, by correctly tracing them to the Monotonicity of the consequence relation. (shrink)

This paper reconstructs the ontological grounding of Aristotle’s logical system as presented in the Prior Analytics, correcting for historical distortions introduced by late antique and medieval commentators, and subsequently by formal logic (Theophrastus, the Latin Organon, and modern Anglo-American analytical traditions). The central claim is that Aristotle’s logic is not a proto-formal calculus of propositions but a conjunctive ontology based on three irreducible axes: Sense (particular / universal) — to whom the benefit of the statement accrues. Form (negation / affirmation) (...) — literal (iconic) vs. abstract (symbolic) understanding. Cause (hypothesis / demonstration) — modal force of the claim. These axes correspond to the eight vertices of a logical cube, which are shown to be isomorphic to the eight generators of the Lie group SU(3) — the symmetry group of strong interaction in particle physics. Each vertex represents an ontological category (e.g., possession, substance, circumstance, quantity, passion, quality, action), and each is expressible as a qubit‑vector in a discrete Hilbert space. The paper formalises the four basic terms of Aristotelian logic — O, I, E, A — as superpositions of two qubits (states: –1, +1/2, 0, +1), and demonstrates that the three figures of the syllogism are not merely syntactic schemata but different topologies of ontological dependence (hierarchical, oppositional, exemplary). A meta‑logical theorem (Khanov’s Noise Theorem) is proved: for combinations of 2 out of 8 categories, the Hilbert lattice contains 64 unique elements, not 125 (noise ≈ –48.8%); for 4 out of 8 (discourse types), 729 elements instead of 4096 (noise ≈ +82.2%); for 8 out of 8 (discursive pixels), 4,913 elements instead of 16,777,216 (noise ≈ +99.97%). This constitutes a mathematical derivation of semantic compression: the difference between purely combinatorial explosion and ontologically constrained possibility spaces. The practical application — KDI (Complex Binary Calculus) — pre‑computes all 4,913 cells during system loading (approx. 5–50 μs). Thereafter, arithmetic and non‑arithmetic operations (addition, multiplication, exponentiation, recognition of narrative structure, DNA transfer markers, musical chords, colour combinations, dialogue trajectories) are reduced to indexed memory access (one clock cycle), rather than processor‑based computation (10–200 cycles for multiplication; billions for semantic inference). For problems that exceed the 17³ base array, the system transitions to a cellular automaton whose computational complexity scales with the field’s diameter, not with bit length. The paper concludes that Aristotelian logic, once restored to its ontological and grammatical ground (the mediopassive participle of being — τὸ ὄν as “that which holds”/“бытующее”), is not a historical relic but an actively superior computational substrate for AI, cryptography, video compression, and deep space communication. The result is a non‑von‑Neumann, non‑Turing ontology machine: one clock cycle per operation regardless of operand size or semantic depth. Keywords: Aristotle, Prior Analytics, syllogism, SU(3), qubit, Hilbert space, ontological categories, KDI, cellular automaton, noise suppression, meta‑logic, non‑Turing computation. (shrink)

Originating in the framework of philosophical preoccupations with paradoxes and determinism, the many-valued logics are today essential, finding abundant applications in STEM fields from electronics to knowledge bases. Essentially characterized by many-valuedness, or the property of having more than the two classical truth values, the many-valued logical systems are often presented only axiomatically and/or truth-functionally, but this presentation largely obliterates the intended meanings of many-truthfulness, the property that in these logics more than a single truth value can be distinguished as (...) true. Matrix semantics, a type of algebraic semantics, handles many-truthfulness in a set-theoretic way that typically allows for a meaning account. In this review article, the core aspects of many-valued logics with matrix semantics are elaborated on from the viewpoint of logical consequence. (shrink)

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 (...) sufficient and necessary conditions to turn a model of into a model of. Moreover, we establish some distinctive semantic properties of. (shrink)

I have developed an Automated Theorem Prover for propositional and quantified, classical and non-classical logics. The software implements and adapts the tableaux proof systems theorized / presented by renowned philosopher and logician Graham Priest in his 2008 book "An Introduction to Non-Classical Logic. From If to Is (2nd edition)". I have extended the software with Łukasiewicz’s fuzzy logic by implementing the tableaux proof system of Olivetti. I have also developed an alternative counter-model finder algorithm for first-order normal modal logics. The (...) software is free and open source. (shrink)

This paper provides a new framework for formalizing conditional obligations in natural language: it pairs a unary deontic operator with trivalent semantics for the indicative conditional and Kratzer's assumption that the antecedents of conditionals restrict the scope of modals in the consequent. Combining these three ideas, we obtain a fully compositional theory of "if" and "ought'" that validates plausible principles for deontic reasoning. Moreover, it resolves classical challenges such as the "if A then ought A" problem, the paradox of the (...) miners and the modeling of contrary-to-duty obligations (e.g., Chisholm's quartet). All in all, our proposal is attractive from a logical point of view and squares well with general theories of natural language reasoning. (shrink)

Resolution Matrix Semantics (RMS) introduces the alternative truth-value-based framework for modal logic, providing a substantive alternative to Kripke’s relational semantics of possible worlds. Drawing inspiration from Y. Ivlev’s substantive semantics, RMS utilizes a 4-valued structure—necessary truth (tn), contingent truth (tc), contingent false (fc), and necessary false (fn)—augmented by indeterminate values (t, f, t/f) to define modal systems Km, KDm, KTm, S4m, and S5m, analogous to Kripke’s K, KD, T, S4, and S5. By directly assigning determined and indeterminate truth values via (...) an interpretation function, RMS validates formulas without relying on accessibility relations, as demonstrated through soundness and completeness proofs and a tailored tableau method. The framework’s versatility extends to applications in deontic logic, artificial intelligence, and quantum computing, enabling context-dependent reasoning with computational efficiency. RMS thus bridges philosophical logic and practical domains, offering a truth-centric perspective on modal reasoning’s complexities. (shrink)

This paper introduces Resolution Matrix Semantics (RMS), a novel framework for modal logic that prioritizes indeterminate truth values and sub-interpretations over traditional relational structures, offering a poly-logic model that mirrors human cognition. Drawing on Vladimir Bibler’s concept of poly-logic substantive control, RMS captures the pluralistic, concurrent nature of human reasoning by evaluating logical formulas across multiple interpretive threads, resolving ambiguities akin to quantum cognitive processes. By integrating insights from quantum cognition, neuroscience, and parallel computing, the paper argues that RMS reflects (...) the brain’s intrinsic ability to navigate uncertainty through superposition-like states and entangled judgments. Philosophically, RMS challenges classical mono-logic assumptions, aligning with non-classical logics and pluralistic epistemologies. Its implications extend to AI, NLP, and quantum computing, promising rapid, precise decision-making under uncertainty. RMS thus redefines rationality as a dynamic, dialogic process, bridging logic, cognition, and the fundamental indeterminacy of reality. (shrink)

Graham Priest distinguishes between two kinds of Sorites paradoxes: standard Sorites, such as the paradox of the Heap, and non-standard Sorites, such as the Ship of Theseus. The former concerns properties of objects, whereas the latter concerns their identity conditions. Priest notes that the standard Sorites has been solved in fuzzy logic and proposes a logic of fuzzy identity to solve the non-standard Sorites in a similar way. Ideally, a definition of fuzzy identity would satisfy the fuzzy equivalents of the (...) classical principles of identity: it should (i) be a fuzzy equivalence relation and (ii) validate a fuzzy version of the substitutivity of identicals. However, Priest’s definition fails to meet the latter requirement and only applies to a special case of the non-standard Sorites. I suggest an improvement on his logic that overcomes these shortcomings, provides the two Sorites with a unified solution, and also applies to reasoning about vague objects in general. (shrink)

Our aim is to provide a sequent calculus whose external consequence relation coincides with the three-valued paracomplete logic ‘of nonsense’ introduced by Dmitry Bochvar and, independently, presented as the weak Kleene logic $$\textbf{K}_{\textbf{3}}^{\textbf{w}}$$ by Stephen C. Kleene. The main features of this calculus are (i) that it is non-reflexive, i.e., Identity is not included as an explicit rule (although a restricted form of it with premises is derivable); (ii) that it includes rules where no variable-inclusion conditions are attached; and (iii) (...) that it is hybrid, insofar as it includes both left and right operational introduction as well as elimination rules. (shrink)

Kripke’s work on modal logic has been immensely influential. It hardly needs remarking that this is not his only work. Here we address his pioneering applications of fixpoint constructions to the theory of truth, and related work by others. In his fundamental paper on this he explicitly described a modal version, applying a fixpoint construction world by world within a modal frame. This can certainly be carried out, and doubtless has been somewhere. Others have suggested a variety of other extensions (...) such as using the unit interval as the underlying space of truth values, or using a four valued logic instead of three, or various combinations of these. When many similar formal constructions have been proposed, one naturally asks what is the common core. Is there some setting in which things can be proved once and for all, with the various specific proposals seen as applications of this common core. In fact this is the case, with bilattices providing the desired structure. Much of such a development has already appeared in some form or other. It is the purpose of this article to bring everything together, and also add a few things. We present general results that, more or less, have everything currently in the fixpoint literature as special cases. Fortunately this does not make things more complicated, since the underlying proofs are essentially the same as they have always been. It is just that they are being carried out in generality rather than in specificity. (shrink)

We give a new and elementary construction of primitive positive decomposition of higher arity relations into binary relations on finite domains. Such decompositions come up in applications to constraint satisfaction problems, clone theory and relational databases. The construction exploits functional completeness of 2-input functions in many-valued logic by interpreting relations as graphs of partially defined multivalued ‘functions’. The ‘functions’ are then composed from ordinary functions in the usual sense. The construction is computationally effective and relies on well-developed methods of functional (...) decomposition, but reduces relations only to ternary relations. An additional construction then decomposes ternary into binary relations, also effectively, by converting certain disjunctions into existential quantifications. The result gives a uniform proof of Peirce’s reduction thesis on finite domains, and shows that the graph of any Sheffer function composes all relations there. (shrink)

Misinformation and biased information significantly impact public perception and political decisions, especially on critical issues such as climate change and environmental conservation. This study aims to understand how indeterminacy and contradiction influence public perception and policy formulation by applying neutrosophic theory to model the complexity and multi-dimensionality of ignorance. Using neutrosophic Likert scales, we capture a nuanced spectrum of opinions on the scientific certainty of human impact on climate change. The results are analyzed through a k-means clustering algorithm to identify (...) patterns and segment participants into groups based on their levels of truth, indeterminacy, and falsehood. This approach reveals deeper insights into public perceptions and aids in evaluating their implications for effective communication and policy-making. (shrink)

Sengzhao (c.374–414) was a Chinese Neo-Daoist who converted to Mahāyāna Buddhism, and few people doubt his influence on Chinese Buddhist philosophy. In this article, provided his Neo-Daoism (xuanxue) and Madhyamaka Buddhism, I will present how Sengzhao featured a symbolic meaning of ‘void’ (śūnya) as rooted originally in Daoism. The Daoist contradictions, in particular between ‘being’ (you) and ‘nothing [non-being]’ (wu), are essential to the development of his doctrine of ‘no ultimate void’ (不真空論, Buzhenkonglun). To understand what Sengzhao meant by ‘void’, (...) which is in denial about the ultimate reality, I broach a notion of nihil (‘nothing’ but also ‘no value’) that bears on his discursive practice. In this light, I formulate a Daoist argument for contradictions and ECN (ex contradictione nihil—nothing follows from contradictions) from Laozi’s Daodejing. Furthermore, I elaborate on Sengzhao’s defence of ECN in his Buzhenkonglun. Reconstructing his negative approach to contradictions within the scope of the four-valued expressions (catuṣkoṭi) in the Madhyamaka tradition from Nāgārjuna, I consider a likely objection that a fifth value such as the ineffable may be inferred as void. Instead of subsuming the ineffable value under his discourse, I finally endorse Sengzhao’s purpose of linguistic and conventional approximation to the ultimate reality as silence. As such, I conclude the significance of void in Sengzhao’s denials via contradictions (ECN), i.e. an early philosophical peak of Chinese Buddhism from Daoism. (shrink)

Noniterative approaches to the sorites paradox accept single steps of soritical reasoning, but deny that these can be combined into valid chains of soritical reasoning. The distributed sorites is a puzzle designed to undermine noniterative approaches to the sorites paradox, by deriving an inconsistent conclusion using only single steps, but not chains, of soritical reasoning. This paper shows how a dialetheist version of the noniterative approach, the strict-tolerant approach, also solves the distributed sorites paradox, at no further cost, by accepting (...) the inconsistent conclusion. (shrink)

In this article we consider argumentation as an epistemic process performed by an agent to extend and revise her beliefs and gain knowledge, according to the information provided by the environment. Such a process can also generate the suspension of the claim under evaluation. How can we account for such a suspension phenomenon in argumentation process? We propose: (1) to distinguish two kinds of suspensions – critical suspension and non-critical suspension – in epistemic change processes; (2) to introduce a Paraconsistent (...) Weak Kleene logic (PWK) based belief revision theory which makes use of the notion of topic to distinguish the two kinds of suspensions previously mentioned, and (3) to develop a PWK-style argumentation framework and its expansion. By doing that, we can distinguish two kinds of suspensions in an epistemic process by virtue of the notion of topic. (shrink)

We present a method that generates two-sided sequent calculi for four-valued logics like "first degree entailment" (FDE). (We say that a logic is FDE-like if it has finitely many operators of finite arity, including negation, and if all of its operators are truth-functional over the four truth-values 'none', 'false', 'true', and 'both', where 'true' and 'both' are designated.) First, we show that for every n-ary operator * every truth table entry f*(x1,...,xn) = y can be characterized in terms of a (...) pair of sequent rules. Secondly, we use these sequent rules to build sequent calculi and prove their completeness. With the help of two simplification procedures we then show that the 2⋅4^n sequent rules that characterize an n-ary operator can be systematically reduced to at most four sequent rules. Thirdly, we use our method to investigate the proof-theoretical consequences of including intuitive truth-functional implications in FDE-like logics. (shrink)

This paper collects and presents unpublished notes of Kurt Gödel concerning the field of many-valued logic. In order to get a picture as complete as possible, both formal and philosophical notes, transcribed from the Gabelsberger shorthand system, are included.

FDE, LP and K3 are closely related to each other and admit of an intuitive informational interpretation. However, all these logics are co-NP complete, and so idealized models of how an agent can think. We address this issue by shifting to signed formulae, where the signs express imprecise values associated with two bipartitions of the corresponding set of standard values. We present proof systems whose operational rules are all linear and have only two structural branching rules that express a generalized (...) Principle of Bivalence. Each of these systems leads to defining an infinite hierarchy of tractable approximations to the respective logic, in terms of the maximum number of allowed nested applications of the two branching rules. Further, each resulting hierarchy admits of an intuitive 5-valued non-deterministic semantics. (shrink)

Angell's logic of analytic containment AC has been shown to be characterized by a 9-valued matrix NC by Ferguson, and by a 16-valued matrix by Fine. We show that the former is the image of a surjective homomorphism from the latter, i.e., an epimorphic image. The epimorphism was found with the help of MUltlog, which also provides a tableau calculus for NC extended by quantifiers that generalize conjunction and disjunction.

Any intermediate propositional logic can be extended to a calculus with epsilon- and tau-operators and critical formulas. For classical logic, this results in Hilbert’s $\varepsilon $ -calculus. The first and second $\varepsilon $ -theorems for classical logic establish conservativity of the $\varepsilon $ -calculus over its classical base logic. It is well known that the second $\varepsilon $ -theorem fails for the intuitionistic $\varepsilon $ -calculus, as prenexation is impossible. The paper investigates the effect of adding critical $\varepsilon $ - (...) and $\tau $ -formulas and using the translation of quantifiers into $\varepsilon $ - and $\tau $ -terms to intermediate logics. It is shown that conservativity over the propositional base logic also holds for such intermediate ${\varepsilon \tau }$ -calculi. The “extended” first $\varepsilon $ -theorem holds if the base logic is finite-valued Gödel–Dummett logic, and fails otherwise, but holds for certain provable formulas in infinite-valued Gödel logic. The second $\varepsilon $ -theorem also holds for finite-valued first-order Gödel logics. The methods used to prove the extended first $\varepsilon $ -theorem for infinite-valued Gödel logic suggest applications to theories of arithmetic. (shrink)

In this paper, we investigate the family LS0.5 of many-valued modal logics LS0.5's. We prove that the modalities of necessity and possibility of the logics LS0.5's capture well-defined bivalent concepts of logical validity and logical consistency. We also show that these modalities can be used as recovery operators.

In order to define some interesting consequence relations, certain generalizations have been proposed in a many-valued semantic setting that have been useful for defining what have been called pure, mixed and ordertheoretic consequence relations. But these generalizations are insufficient to capture some other interesting relations, like other intersective mixed relations (a relation that cannot be defined as a mixed relation, but only as the intersection of two mixed relations) or relations with a conjunctive (or, better, “universal”) interpretation for multiple conclusions. (...) We propose a broader framework to define these cases, and many others, and to set a common background that allows for a direct compared analysis. At the end of the work, we illustrate some of these comparisons. (shrink)

Despite being fairly powerful, finite non-deterministic matrices are unable to characterize some logics of formal inconsistency, such as those found between mbCcl and Cila. In order to overcome this limitation, we propose here restricted non-deterministic matrices (in short, RNmatrices), which are non-deterministic algebras together with a subset of the set of valuations. This allows us to characterize not only mbCcl and Cila (which is equivalent, up to language, to da Costa's logic C_1) but the whole hierarchy of da Costa's calculi (...) C_n. This produces a novel decision procedure for these logics. Moreover, we show that the RNmatrix semantics proposed here induces naturally a labelled tableau system for each C_n, which constitutes another decision procedure for these logics. This new semantics allows us to conceive da Costa's hierarchy of C-systems as a family of (non deterministically) (n+2)-valued logics, where n is the number of "inconsistently true" truth-values and 2 is the number of "classical" or "consistent" truth-values, for every C_n. (shrink)

In 2001, W. Carnielli and Marcos considered a 3-valued logic in order to prove that the schema ϕ ∨ (ϕ → ψ) is not a theorem of da Costa’s logic Cω. In 2006, this logic was studied (and baptized) as G'3 by Osorio et al. as a tool to define semantics of logic programming. It is known that the truth-tables of G'3 have the same expressive power than the one of Łukasiewicz 3-valued logic as well as the one of Gödel (...) 3-valued logic G3. From this, the three logics coincide up-to language, taking into acccount that 1 is the only designated truth-value in these logics. -/- From the algebraic point of view, Canals-Frau and Figallo have studied the 3-valued modal implicative semilattices, where the modal operator is the well-known Moisil-Monteiro-Baaz Δ operator, and the supremum is definable from this. We prove that the subvariety obtained from this by adding a bottom element 0 is term-equivalent to the variety generated by the 3-valued algebra of G'3. The algebras of that variety are called G'3-algebras. From this result, we obtain the equations which axiomatize the variety of G'3-algebras. Moreover, we prove that this variety is semisimple, and the 3-element and the 2-element chains are the unique simple algebras of the variety. Finally an extension of G'3 to first-order languages is presented, with an algebraic semantics based on complete G'3-algebras. The corresponding soundness and completeness theorems are obtained. (shrink)

The logics RŁ, RP, and RG have been obtained by expanding Łukasiewicz logic Ł, product logic P, and Gödel–Dummett logic G with rational constants. We study the lattices of extensions and structural completeness of these three expansions, obtaining results that stand in contrast to the known situation in Ł, P, and G. Namely, RŁ is hereditarily structurally complete. RP is algebraized by the variety of rational product algebras that we show to be Q-universal. We provide a base of admissible rules (...) in RP, show their decidability, and characterize passive structural completeness for extensions of RP. Furthermore, structural completeness, hereditary structural completeness, and active structural completeness coincide for extensions of RP, and this is also the case for extensions of RG, where in turn passive structural completeness is characterized by the equivalent algebraic semantics having the joint embedding property. For nontrivial axiomatic extensions of RG, we provide a base of admissible rules. We leave the problem open whether the variety of rational Gödel algebras is Q-universal. (shrink)

Graham Priest has formulated the minimally inconsistent logic of paradox (MiLP), which is paraconsistent like Priest’s logic of paradox (LP), while staying closer to classical logic. We present logics that stand to (the propositional fragments of) strong Kleene logic (K3) and the logic of first-degree entailment (FDE) as MiLP stands to LP. That is, our logics share the paracomplete and the paraconsistent-cum-paracomplete nature of K3 and FDE, respectively, while keeping these features to a minimum in order to stay closer to (...) classical logic. We give semantic and sequent-calculus formulations of these logics, and we highlight some reasons why these logics may be interesting in their own right. (shrink)