Classical Logic

Our usual explication of a logic through an axiomatic calculus is structurally _foundationalist_. Justification gets transferred by applying rules finitely many times from already justified sentences to new sentences in a linear-like fashion, by starting from a base of non-to-be justified sentences (i.e. the axioms). In contrast, this paper develops a _coherentist approach_ to _classical propositional logic_, by explaining the fundamental notion of deducibility in terms of a primitive notion of _logical coherence_. This is done by introducing a calculus consisting (...) of rules that capture the properties of classical consistency. The basic logical reasoning process explicated is that of constructing consistent sets of formulas. I show how to define classical deducibility in terms of the primitive relation of logical coherence. As applications, I use the coherence calculus to provide a non-semantic proof of the consistency of an axiomatic calculus for classical propositional logic, I show how the system avoids an impossibility result for semantic resemblance proven by Leitgeb, I show that the strategy of defining deducibility from coherence does not work for intuitionistic logic and I briefly compare my approach to the Simple Theory of Propositions put forward by Stalnaker and Fritz. (shrink)

Bob and Ulf say logic should make explicit / The kinds of inference we take as licit. / They give a formalism that’s classically complete, / But in which an extra premise may defeat / An inference that seems a reasonable fact. / Thus reason’s made explicit but is it exact? / For reason in the sense of Brandom and Hlobil, / May explode like a logical Chernobyl. / This is the point on which I’d like to push back, / (...) And keep the game of giving reasons exact. / So with the help of fancy formal antics, / I’ll give nonmonotonic truthmaker semantics. (shrink)

This article aims to study, proof-theoretically and semantically, Gentzen-style sequent calculi (including possibly Cut-free and Identity-free systems), containing combinations of canonical and cocanonical rules, i.e. Gentzen systems for sequents, with well-behaved forms of left and right introduction and elimination rules for logical expressions. Our main goals are to provide soundness and completeness results for the derivability relations of the target systems in terms of 2-, 3-, or 4-valued non-deterministic semantics, and to give sufficient conditions under which these calculi are prone (...) to produce well-behaved normal derivations of a structurally-atomic analytic-synthetic kind. (shrink)

Peirce made three discoveries and left them apart. He named abduction, the only inference that introduces a new idea. He found that NAND — what he called the ampheck — is logically complete, the single connective from which all others derive. In his existential graphs he reduced logic to a single primitive: the cut, a closed curve, one negation. He never joined these findings. Joining them changes what abduction does. When the observer's distinctions are made the input rather than the (...) frame, the operation stops generating hypotheses and begins eliminating them. What cannot be eliminated without collapsing a real distinction is the remainder. When every candidate is eliminated, the output is silence — which is not failure but a specific kind of information. These are things Peirce had the equipment to say. (shrink)

The purpose of the paper is to answer the question of what additional existential premises are needed in order to render Aristotelian syllogisms provable in First-Order Logic and to give an overview of how the issue of ontological commitments in syllogistic was handled throughout the history. In contemporary discussions concerning the history of logic, there is a widespread assumption that the Aristotelian syllogistic, as it is the case with the modern formal logic, did not allow for the use of empty (...) terms. The issue is however much more complex, and ontological commitments of syllogistic were discussed extensively throughout the history. In the paper, we relate these discussions, covering four main areas: the logic of Aristotle, Arabic logic, medieval European logic, and later discussions up till the emergence of modern formal logic, as well as provide our own view of the issue. (shrink)

I show that Hanoch Ben-Yami's so-called QUantified ARgument Calculus (QUARC) can be extended to what I call QUARC+ which I show to be intertranslatable with a version of first-order logic in which unary predicates are non-empty. Given this result, I show that QUARC+ is complete, propose an axiomatization of QUARC, and discuss the resulting expressive limitation of QUARC.

This paper begins from a question that arose while thinking about the fact that classical logical paradoxes have been refuted not by logic but by mathematics. I began to wonder whether such refutations can truly be called logical ones. If a paradox is constructed through logic—through language—can a mathematical refutation really be said to refute the essence of that logic? -/- The author begins this paper with the personal thought and view that a logical paradox expressed through language must likewise (...) be refuted by uncovering the logical contradiction within that language. Only then can it truly be said that the logic has been refuted. (shrink)

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 (...) describes. From this minimal commitment, the three classical laws follow necessarily: identity from the self-definition of SP against IP; non-contradiction from the antithetical nature of the two poles; excluded middle from the binary’s admission of no third value. The paper engages Graham Priest’s defense of paraconsistent logic and W.V.O. Quine’s contingency thesis as the two most direct challenges, arguing that both presuppose the binary they attempt to revise. No further metaphysical commitments are required beyond the co-primordial structure itself. (shrink)

In this essay, I prove two general recapture theorems (the GRT and the $$\textbf{GRT}^\textsf{Dual}$$ GRT Dual ). Each of these states that any sub-logic of classical logic that is closed under six rules of inference is equivalent, in the relevant sense, to classical logic. After proving in each case that the six rules in question are independent of one another, and exploring a number of possible modifications or extensions of these results, I compare the results to Jc Beall’s recapture results (...) in Beall (2011), Beall (2013a) and Beall (2013b). The GRT (and $$\textbf{GRT}^\textsf{Dual}$$ GRT Dual ) are shown to be more powerful and general than Beall’s more piecemeal approach. (shrink)

Hinge propositions—or simply “hinges”—are primitive certainties that we (must) presuppose to enable our entire belief systems. Recently there has been a lot of interest in hinge epistemology, which is a kind of epistemology that sets the notion of hinge at the center stage. This paper puts forward a dilemma levelled against hinge epistemologists. The dilemma is based on work by Pascal Engel (2016) and states that, given the assumption that hinge propositions are normative at all, they are either non-epistemic grammatical (...) norms or epistemic norms. If the former is the case, hinges would appear to be irrelevant to epistemology as it is ordinarily conceived, while if the latter holds, the result would be an incomprehensible hinge epistemology altogether. After presenting Engel’s dilemma (§§1-2), it is utilized to tease out certain puzzling insights about the epistemic significance of logical disagreement (§§3-4). (shrink)

The paper examines the interplay of classical concept theory, Buddhist philosophy, and Russian metaphysics, focusing on the inverse relationship between a concept’s content and extension. It shows that a concept with infinite content, including contradictory attributes, has a null extension, making it “empty.” This is interpreted through Buddhist śūnyatā (Madhyamaka, Diamond Sutra) and linked to Solovyov’s “all-unity” and Florensky’s “antinomy.” Using non-classical logic (dialectical, multi-valued, quantum), it establishes the equivalence of “everything” and “nothing.” The analysis connects these ideas across philosophical (...) traditions and highlights their relevance to modern science, including ecology, AI, and complex systems. (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)

First published in 1997. Routledge is an imprint of Taylor & Francis, an informa company.

This article introduces a modal-tensed logic of actualization, grounded in a processual and non-metrical ontology of the real. Classical modal logics evaluate truth across pre-constituted possible worlds, treating modality as extensional and symmetric. In contrast, we propose that modality arises from the internal dynamics of stabilization within a field of tensions: configurations become possible, effective, or actual according to their capacity to resolve constraints. The logic defines five operators, present actualization, past trace, future projection, structural possibility, and necessity, governed by (...) axioms encoding irreversibility, fragility, and asymmetrical transition. We provide a semantic model based on dynamically accessible configurations with intensity-based stabilization. A case study in quantum measurement illustrates how actualization captures the transition from superposition to definite outcome without invoking collapse. This framework reconceptualizes modality, temporality, and ontology as emergent from internal dynamics rather than imposed from external metaphysical structures. It offers new perspectives on metaphysical logic and the foundations of physics. (shrink)

Start with an extension of Q (Robinson arithmetic) that internalizes an axiom predicate, and has an axiom that denies axiom-status to a formula using a constant $\alpha$. Then, whether the system is consistent depends on which number is assigned to $\alpha$. Contradiction is provable if $\alpha$ is ``directly'' self-referential as per recent work by Kripke. The contradiction is structurally akin to the liar paradox but arises without the usual semantic or modal vocabulary. Several solutions are noted. Yet it remains that (...) axiomhood exhibits liar-like fragility under naive internalization. (shrink)

Structuralism is one of the most popular contemporary accounts of mathematics. Despite its popularity, it has been challenged on the grounds of consistency. In this paper, I show that existing arguments purporting to establish an inconsistency miss the mark. I then proceed to develop a new argument against realist structuralism, to show that the commitment to mathematical pluralism and the structural identity criterion embraced by the realist structuralist jointly entail a contradiction.

The aim of this article is to show that, just as in recent years Cobreros, Egré, Ripley and van Rooij have provided a non-transitive counterpart of classical logic (i.e. one in which all classically acceptable inferences are valid but Cut and other metainferences are not), the same can be done for every Tarskian logic, with full generality. To establish this fact, a semantic approach is taken by showing that appropriate structures can be devised to characterize a non-transitive counterpart of every (...) Tarskian logic, starting from the logical matrices that are usually taken to render them. (shrink)

Bilateral proof systems, which provide rules for both affirming and denying sentences, have been prominent in the development of proof-theoretic semantics for classical logic in recent years. However, such systems provide a substantial amount of freedom in the formulation of the rules, and, as a result, a number of different sets of rules have been put forward as definitive of the meanings of the classical connectives. In this paper, I argue that a single general schema for bilateral proof rules has (...) a reasonable claim to inferentially articulating the core meaning of all of the classical connectives. I propose this schema in the context of a bilateral sequent calculus in which each connective is given exactly two rules: a rule for affirmation and a rule for denial. Positive and negative rules for all of the classical connectives are given by a single rule schema, harmony between these positive and negative rules is established at the schematic level by a pair of elimination theorems, and the truth-conditions for all of the classical connectives are read off at once from the schema itself. (shrink)

A consequence relation is strongly classical if it has all the theorems and entailments of classical logic as well as the usual meta-rules (such as Conditional Proof). A consequence relation is weakly classical if it has all the theorems and entailments of classical logic but lacks the usual meta-rules. The most familiar example of a weakly classical consequence relation comes from a simple supervaluational approach to modelling vague language. This approach is formally equivalent to an account of logical consequence according (...) to which α1, ..., αn entails β just in case □α1, ..., □αn entails □β in the modal logic S5. This raises a natural question: If we start with a different underlying modal logic, can we generate a strongly classical logic? This paper explores this question. In particular, it discusses four related technical issues: (1) Which base modal logics generate strongly classical logics and which generate weakly classical logics? (2) Which base logics generate themselves? (3) How can we directly characterize the logic generated from a given base logic? (4) Given a logic that can be generated, which base logics generate it? The answers to these questions have philosophical interest. They can help us to determine whether there is a plausible supervaluational approach to modelling vague language that yields the usual meta-rules. They can also help us to determine the feasibility of other philosophical projects that rely on an analogous formalism, such as the project of defining logical consequence in terms of the preservation of an epistemic status. (shrink)

Each many-sorted theory can be converted to an unsorted theory. But this conversion procedure is not uniquely determined, leading to a dilemma: which unsorted theory captures the content of the corresponding many-sorted theory?

This chapter contains sections titled: What is Paraconsistency? Motives for Paraconsistency The Sources of Trivialization A Natural Taxonomy for Paraconsistent Logics Paraconsistent Logics Current Issues.

A metainference is usually understood as a pair consisting of a collection of inferences, called premises, and a single inference, called conclusion. In the last few years, much attention has been paid to the study of metainferences—and, in particular, to the question of what are the valid metainferences of a given logic. So far, however, this study has been done in quite a poor language. Our usual sequent calculi have no way to represent, e.g. negations, disjunctions or conjunctions of inferences. (...) In this paper we tackle this expressive issue. We assume some background sentential language as given and define what we call an inferential language, that is, a language whose atomic formulas are inferences. We provide a model-theoretic characterization of validity for this language—relative to some given characterization of validity for the background sentential language—and provide a proof-theoretic analysis of validity. We argue that our novel language has fruitful philosophical applications. Lastly, we generalize some of our definitions and results to arbitrary metainferential levels. (shrink)

This paper explores an idea of Stoic descent that is largely neglected nowadays, the idea that an argument is valid when the conditional formed by the conjunction of its premises as antecedent and its conclusion as consequent is true. As it will be argued, once some basic features of our naıve understanding of validity are properly spelled out, and a suitable account of conditionals is adopted, the equivalence between valid arguments and true conditionals makes perfect sense. The account of validity (...) outlined here, which displays one coherent way to articulate the Stoic intuition, accords with standard formal treatments of deductive validity and encompasses an independently grounded characterization of inductive validity. (shrink)

In this paper we treat metasequents—objects which stand to sequents as sequents stand to formulas—as first class logical citizens. To this end we provide a metasequent calculus, a sequent calculus which allows us to directly manipulate metasequents. We show that the various metasequent calculi we consider are sound and complete w.r.t. appropriate classes of tetravaluations where validity is understood locally. Finally we use our metasequent calculus to give direct syntactic proofs of various collapse results, closing a problem left open in (...) French (Ergo, 3(5), 113–131 2016). (shrink)

Bilateralists, who accept that there are two primitive speech acts, assertion and denial, can offer an attractive definition of consequence: Y follows from X if and only if it is incoherent to assert all formulas X and to deny all formulas Y. The present paper argues that this definition has consequences many will find problematic, amongst them that truth coincides with assertibility. Philosophers who reject these consequences should therefore reject this definition of consequence.

We introduce a new family of jump operators on Borel equivalence relations; specifically, for each countable group [Formula: see text] we introduce the [Formula: see text]-jump. We study the elementary properties of the [Formula: see text]-jumps and compare them with other previously studied jump operators. One of our main results is to establish that for many groups [Formula: see text], the [Formula: see text]-jump is proper in the sense that for any Borel equivalence relation [Formula: see text] the [Formula: see (...) text]-jump of [Formula: see text] is strictly higher than [Formula: see text] in the Borel reducibility hierarchy. On the other hand, there are examples of groups [Formula: see text] for which the [Formula: see text]-jump is not proper. To establish properness, we produce an analysis of Borel equivalence relations induced by continuous actions of the automorphism group of what we denote the full [Formula: see text]-tree, and relate these to iterates of the [Formula: see text]-jump. We also produce several new examples of equivalence relations that arise from applying the [Formula: see text]-jump to classically studied equivalence relations and derive generic ergodicity results related to these. We apply our results to show that the complexity of the isomorphism problem for countable scattered linear orders properly increases with the rank. (shrink)

This paper discusses the theoretical assumptions behind the conception of the logic of faith and deed and outlines its formal-axiomatic frame and its method of construction, which enable us to understand it as a kind of deductive science. The paper is divided into several sections, starting with the logical analysis of the ambiguous terms of ‚faith’ and ‚action’, and focusing in particular on the concepts of religious faith and deed as a type of conscious activity relating to a matter or (...) matters of social importance. After outlining the main ideas and basic assumptions of the theoretical conception of the LF&D as an axiomatic theory, the author introduces some axiom systems for: 1) the logics of faith LF, 2) the logic of deed LD, and 3) certain logics of norms DL connected with „duties” and concerning actions/deeds. Lastly, the paper outlines the scientific LF&D based on the three types of logic 1)–3). (shrink)

Planlama --- bir amaca ulaşmak üzere bir aksiyonlar bütünü tasarlamak --- yapay zekadaki en temel problemlerden biridir. Bu yazıda, robotikte planlama konusuna mantıkçı (logicist) yaklaşım ele alınmaktadır. [Planning --- devising a plan of action to reach a given goal --- is a fundamental problem in AI. This paper reviews the logicist approach to planning in robotics.].

One of the main controversies of the Logic Schools of the 12th century centered on the question: What follows from the impossible? In this paper arguments for two diametrically opposed positions are examined. The author of the ‘Avranches Text’ who probably belonged to the school of the Parvipontani defended the view that from an impossible proposition everything follows (‘Ex impossibili quodlibet’). In particular he developed a proof to show that by means of so-called ‘disjunctive syllogism’ any arbitrary proposition B can (...) be logically derived from a pair of contradictory propositions A and Not-A. The author of the Ars Meliduna instead argued that nothing follows from an impossible proposition (‘ex falso nihil sequitur’). This view is supported by various counterexamples which aimed to show that the admission of impossible premises would give rise to inconsistent conclusions. Upon closer analysis these inconsistencies do not, however, have the formal structure of a real contradiction like A and Not-A, but rather the structure of two rivalling conditionals like ‘If B then A’ and ‘If B then Not-A’. Hence these counterexamples rather have to be considered as refutations of the basic principles of ‘connexive logic’. (shrink)

Formalizing categorical propositions of traditional logic in the language of quantifiers and propositional functions is no straightforward matter, especially when modalities get involved. Starting...

A number of medieval Arabic logicians discussed inferences that combine the principles of propositional and term logic, for example: Whenever H is Z then Every J is DNo D is AWhenever H is Z then S...

In his Doppelvortrag, Edmund Husserl introduced two concepts of “definiteness” which have been interpreted as a vindication of his role in the history of completeness. Some commentators defended that the meaning of these notions should be understood as categoricity, while other scholars believed that it is closer to syntactic completeness. A detailed study of the early twentieth-century axiomatics and Husserl’s Doppelvortrag shows, however, that many concepts of completeness were conflated as equivalent. Although “absolute definiteness” was principally an attempt to characterize (...) non-extendible manifolds and axiom systems, an absolutely definite theory has a unique model and, thus, it is non-forkable and semantically complete. Non-forkability and decidability were formally delimited by Fraenkel and Carnap almost three decades later and, in fact, they mentioned Husserl as precursor of the latter. Therefore, this paper contributes to a reassessment of Husserl’s place in the history of logic. (shrink)

We generalize the notion of analytic/Borel equivalence relations, orbit equivalence relations, and Borel reductions between them to their continuous and quantitative counterparts: analytic/Borel pseudometrics, orbit pseudometrics, and Borel reductions between them. We motivate these concepts on examples and we set some basic general theory. We illustrate the new notion of reduction by showing that the Gromov–Hausdorff distance maintains the same complexity if it is defined on the class of all Polish metric spaces, spaces bounded from below, from above, and from (...) both below and above. Then we show that [Formula: see text] is not reducible to equivalences induced by orbit pseudometrics, generalizing the seminal result of Kechris and Louveau. We answer in negative a question of Ben Yaacov, Doucha, Nies, and Tsankov on whether balls in the Gromov–Hausdorff and Kadets distances are Borel. In appendix, we provide new methods using games showing that the distance-zero classes in certain pseudometrics are Borel, extending the results of Ben Yaacov, Doucha, Nies, and Tsankov. There is a complementary paper of the authors where reductions between the most common pseudometrics from functional analysis and metric geometry are provided. (shrink)

"Philosophical logic" describes two distinct areas: the investigation of the fundamental concepts of logic, the formal investigation of alternatives and extensions to classical logic. The first is a philosophical discipline, concerned with notions like truth, propositions, necessity, logical consequence, vagueness, and reasoning. The second is a technical discipline, devoted to developing formal logical systems-modal logics, second-order logics, intuitionistic logics, relevance logics, logics of vagueness and conditionals-and proving things about them. Most texts in philosophical logic focus on one of these areas, (...) but in this book John MacFarlane treats them together in an integrated way, showing how philosophical considerations motivate the technical projects, and how the constraints revealed by the technical projects illuminate the philosophical issues. Topics covered include quantifiers, modal logic, indicative conditionals, model-theoretic and proof-theoretic characterizations of logical consequence, intuitionistic logic, fundamental logical disagreement, relevance logic, the relation of logic and reasoning, and vagueness. Each chapter is organized around suggested readings and includes exercises. Key Features: An integrated treatment of the technical and philosophical issues comprising philosophical logic Written by a leading authority on logicism and logical form and a successful expositor and teacher Designed to serve students taking only one course in logic beyond the introductory level Provides tools and concepts necessary to understand work in many areas of analytic philosophy Includes exercises, suggested readings, and suggestions for further exploration in each chapter. (shrink)

We prove that the two-variable fragment of first-order logic has the weak Beth definability property. This makes the two-variable fragment a natural logic separating the weak and the strong Beth properties since it does not have the strong Beth definability property.

Drawing on the analogy between any unary first-order quantifier and a "face operator," this paper establishes several connections between model theory and homotopy theory. The concept of simplicial set is brought into play to describe the formulae of any first-order language L, the definable subsets of any L-structure, as well as the type spaces of any theory expressed in L. An adjunction result is then proved between the category of o-minimal structures and a subcategory of the category of linearly ordered (...) simplicial sets with distinguished vertices. (shrink)

We examine the set of formula-to-formula valid inferences of Classical Logic, where the premise and the conclusion share at least a propositional variable in common. We review the fact, already proved in the literature, that such a system is identical to the first-degree entailment fragment of R. Epstein's Relatedness Logic, and that it is a non-transitive logic of the sort investigated by S. Frankowski and others. Furthermore, we provide a semantics and a calculus for this logic. The semantics is defined (...) in terms of a \-matrix built on top of a 5-valued extension of the 3-element weak Kleene algebra, whereas the calculus is defined in terms of a Gentzen-style sequent system where the left and right negation rules are subject to linguistic constraints. (shrink)

We present four classical theories of counterpossibles that combine modalities and counterfactuals. Two theories are anti-vacuist and forbid vacuously true counterfactuals, two are quasi-vacuist and allow counterfactuals to be vacuously true when their antecedent is not only impossible, but also inconceivable. The theories vary on how they restrict the interaction of modalities and counterfactuals. We provide a logical cartography with precise acceptable boundaries, illustrating to what extent nonvacuism about counterpossibles can be reconciled with classical logic.

In this thesis, we will study the embedding of classical first-order logic in first-order S4, which is based on the translation originally introduced in Fitting (1970). The initial main part is dedicated to a detailed model-theoretic proof of the soundness of the embedding. This will follow the proof sketch in Fitting (1970). We will then outline a proof procedure for a proof-theoretic replication of the soundness result. Afterwards, a potential proof of faithfulness of the embedding, read in terms of soundness (...) and completeness, will be discussed. We will particularly highlight the many difficulties coming with it. In the final section, we will relate this discussion to the debate on notational variance in French (2019). We will do this by showing how a weaker version of French's notion of ‘expressive equivalence’ conforms to the model-theoretic soundness result. We will then conclude that the soundness result without completeness might contain rather little overall insight by relating it to the extensibility of classical logic to S4. (shrink)

We present an axiomatization of the non-associative Lambek calculus extended with classical negation for which the frame semantics with the classical interpretation of negation is sound and complete.

The paper presents Alfred Tarski’s debate with the semantic antinomies: the basic Liar Paradox, and its more sophisticated versions, which are currently discussed in philosophy: Strengthen Liar Paradox, Cyclical Liar Paradox, Contingent Liar Paradox, Correct Liar Paradox, Card Paradox, Yablo’s Paradox and a few others. Since Tarski, himself did not addressed these paradoxes—neither in his famous work published in 1933, nor in later papers in which he developed the Semantic Theory of Truth—therefore, We try to defend his concept of truth (...) against these antinomies. It is demonstrated that Tarskian theory of truth is resistant to the paradoxes and it is still the best solution to avoid the antinomies and remain within a classical logic, that is, accepting the laws of noncontradiction, excluded middle, and the principle of bivalence. Thus, the goal of the paper is double—firstly, to show that none of the versions of the Liar Paradox’s is a serious threat to Tarski’s concept of truth, and secondly, that Semantic Theory of Truth allows to remain within classical logic, and at the same time, avoid antinomies—which makes it the most attractive among classical theories of truth. (shrink)

This paper and its sequel “look under the hood” of the usual sorts of proof-theoretic systems for certain well-known intuitionistic and classical propositional modal logics. Section 1 is preliminary. Of most importance: a marked formula will be the result of prefixing a formula in a propositional modal language with a step-marker, for this paper either 0 or 1. Think of 1 as indicating the taking of “one step away from 0.” Deductions will be constructed using marked formulas. Section 2 presents (...) the model-theoretic concepts, based on those in [7], that guide the rest of this paper. Section 3 presents Natural Deduction systems IK and CK, formalizations of intuitionistic and classical one-step versions of K. In these systems, occurrences of step-markers allow deductions to display deductive structure that is covered over in familiar “no step” proof-theoretic systems for such logics. Box and Diamond are governed by Introduction and Elimination rules; the familiar K rule and Necessitation are derived (i.e. admissible) rules. CK will be the result of adding the 0-version of the Rule of Excluded Middle to the rules which generate IK. Note: IK is the result of merely dropping that rule from those generating CK, without addition of further rules or axioms (as was needed in [7]). These proof-theoretic systems yield intuitionistic and classical consequence relations by the obvious definition. Section 4 provides some examples of what can be deduced in IK. Section 5 defines some proof-theoretic concepts that are used in Section 6 to prove the soundness of the consequence relation for IK (relative to the class of models defined in Section 2.) Section 7 proves its completeness (relative to that class). Section 8 extends these results to the consequence relation for CK. (Looking ahead: Part 2 will investigate one-step proof-theoretic systems formalizing intuitionistic and classical one-step versions of some familiar logics stronger than K.). (shrink)

We present a generalization of the algebra-valued models of \ where the axioms of set theory are not necessarily mapped to the top element of an algebra, but may get intermediate values, in a set of designated values. Under this generalization there are many algebras which are neither Boolean, nor Heyting, but that still validate \.

In this study, falsification-aware semantics and sequent calculi for first-order classical logic are introduced and investigated. These semantics and sequent calculi are constructed based on a falsification-aware setting for first-order Nelson constructive three-valued logic. In fact, these semantics and sequent calculi are regarded as those for a classical variant of N3. The completeness and cut-elimination theorems for the proposed semantics and sequent calculi are proved using Schütte’s method. Similar results for the propositional case are also obtained.

It is widely accepted that classical logic is trivialized in the presence of a transparent truth-predicate. In this paper, we will explain why this point of view must be given up. The hierarchy of metainferential logics defined in Barrio et al. and Pailos recovers classical logic, either in the sense that every classical inferential validity is valid at some point in the hierarchy ), or because a logic of a transfinite level defined in terms of the hierarchy shares its validities (...) with classical logic. Each of these logics is consistent with transparent truth—as is shown in Pailos —, and this suggests that, contrary to standard opinions, transparent truth is after all consistent with classical logic. However, Scambler presents a major challenge to this approach. He argues that this hierarchy cannot be identified with classical logic in any way, because it recovers no classical antivalidities. We embrace Scambler’s challenge and develop a new logic based on these hierarchies. This logic recovers both every classical validity and every classical antivalidity. Moreover, we will follow the same strategy and show that contingencies need also be taken into account, and that none of the logics so far presented is enough to capture classical contingencies. Then, we will develop a multi-standard approach to elaborate a new logic that captures not only every classical validity, but also every classical antivalidity and contingency. As a€truth-predicate can be added to this logic, this result can be interpreted as showing that, despite the claims that are extremely widely accepted, classical logic does not trivialize in the context of transparent truth. (shrink)