Logics Of Formal Inconsistency Research Articles

Intuitionistic Implication and Logics of Formal Inconsistency

Logics of Formal Inconsistency (LFI for short) are a class of paraconsistent logics that validate the principle of gentle explosion, meaning that any formula can be derived from the set of formulas: ∘α, α and ∼α. A unique feature of LFI is the use of the symbol ‘∘’ to represent notions of consistency at the object-language level. These logics are simple in essence, built upon all the axiom schemas of positive classical logic, axioms for negation and the so-called ‘consistency operator’ ∘, with the only inference rule being detachment. In this paper, we propose an alternative foundation for LFI, which is the positive fragment of intuitionistic propositional logic. We present bi-valuational ‘Loparić-like’ semantics for the resulting logics and discuss their potential extensions.

Truth diagrams for some non-classical and modal logics

This paper examines truth diagrams for some non-classical, modal and dynamic logics. Truth diagrams are diagrammatic and visual ways to represent logical truth akin to truth tables, developed by Peter C.-H. Cheng. Currently, it is only given for classical propositional logic. In this paper, we establish truth diagrams for Priest's Logic of Paradox, Belnap–Dunn's Four-Valued Logic, MacColl's Connexive Logic, Bochvar–Halldén's Logic of Non-Sense, Carnielli–Coniglio's logic of formal inconsistency as well as classical modal logic and its dynamic extension to shed light on the semantic behaviour of some non-classical and modal logics.

Paraconsistency in Non-Fregean Framework

AbstractA non-Fregean framework aims to provide a formal tool for reasoning about semantic denotations of sentences and their interactions. Extending a logic to its non-Fregean version involves introducing a new connective $$\equiv $$ ≡ that allows to separate denotations of sentences from their logical values. Intuitively, $$\equiv $$ ≡ combines two sentences $$\varphi $$ φ and $$\psi $$ ψ into a true one whenever $$\varphi $$ φ and $$\psi $$ ψ have the same semantic correlates, describe the same situations, or have the same content or meaning. The paper aims to compare non-Fregean paraconsistent Grzegorczyk’s logics (Logic of Descriptions $$\textsf{LD}$$ LD , Logic of Descriptions with Suszko’s Axioms $$\textsf{LDS}$$ LDS , Logic of Equimeaning $$\textsf{LDE}$$ LDE ) with non-Fregean versions of certain well-known paraconsistent logics (Jaśkowski’s Discussive Logic $$\textsf{D}_2$$ D 2 , Logic of Paradox $$\textsf{LP}$$ LP , Logics of Formal Inconsistency $$\textsf{LFI}{1}$$ LFI 1 and $$\textsf{LFI}{2}$$ LFI 2 ). We prove that Grzegorczyk’s logics are either weaker than or incomparable to non-Fregean extensions of $$\textsf{LP}$$ LP , $$\textsf{LFI}{1}$$ LFI 1 , $$\textsf{LFI}{2}$$ LFI 2 . Furthermore, we show that non-Fregean extensions of $$\textsf{LP}$$ LP , $$\textsf{LFI}{1}$$ LFI 1 , $$\textsf{LFI}{2}$$ LFI 2 , and $$\textsf{D}_2$$ D 2 are more expressive than their original counterparts. Our results highlight that the non-Fregean connective $$\equiv $$ ≡ can serve as a tool for expressing various properties of the ontology underlying the logics under consideration.

Cut-free sequent-style systems for a logic associated to involutive Stone algebras

Abstract In [4, 5], it was introduced a logic (called Six) associated to a class of algebraic structures known as involutive Stone algebras. This class of algebras, denoted by S, was considered by the first time in [6] as a tool for the study of certain problems connected to the theory of finite-valued Łukasiewicz–Moisil algebras. In fact, Six is the logic that preserves degrees of truth with respect to the class S. Among other things, it was proved that Six is a 6-valued logic that is a Logic of Formal Inconsistency (LFI ); moreover, it is possible to define a consistency operator in terms of the original set of connectives. A Gentzen-style system (which does not enjoy the cut-elimination property) for Six was given. Besides, in [5], it was shown that Six is matrix logic that is determined by a finite number of matrices; more precisely, four matrices. However, this result was further sharpened in [17], proving that just one of these four matrices determine Six, i.e. Six can be determined by a single 6-element logic matrix. In this work, taking advantage of this last result, we apply a method due to Avron, Ben-Naim and Konikowska [3] to present different Gentzen systems for Six enjoying the cut-elimination property. This allows us to draw some conclusions about the method as well as to propose additional tools for the streamlining process. Finally, we present a decision procedure for Six based in one of these systems.

From Inconsistency to Incompatibility

The aim of this article is to generalize logics of formal inconsistency (LFIs) to systems dealing with the concept of incompatibility, expressed by means of a binary connective. The basic idea is that having two incompatible formulas to hold trivializes a deduction, and as a special case, a formula becomes consistent (in the sense of LFIs) when it is incompatible with its own negation. We show how this notion extends that of consistency in a non-trivial way, presenting conservative translations for many simple LFIs into some of the most basic logics of incompatibility, thereby evidencing in a precise way how the notion of incompatibility generalizes that of consistency. We provide semantics for the new logics, as well as decision procedures, based on restricted non-deterministic matrices. The use of non-deterministic semantics with restrictions is justified by the fact that, as proved here, these systems are not algebraizable according to Blok-Pigozzi nor are they characterizable by finite Nmatrices. Finally, we briefly compare our logics to other systems focused on treating incompatibility, specially those pioneered by Brandom and further developed by Peregrin.

Non-Deterministic Matrices: Theory and Applications to Algebraic Semantics

AbstractWe call multioperation any operation that return for even argument a set of values instead of a single value. Through multioperations we can define an algebraic structure equipped with at least one multioperation. This kind of structure is called multialgebra. The study of them began in 1934 with the publication of a paper of Marty. In the realm of Logic, multialgebras were considered by Avron and his collaborators under the name of non-deterministic matrices (or Nmatrices) and used as semantics tool for characterizing some logics which cannot be characterized by a single finite matrix. Carnielli and Coniglio introduced the semantics of swap structures for LFIs (Logics of Formal Inconsistency), which are Nmatrices defined over triples in a Boolean algebra, generalizing Avron’s semantics. In this thesis, we will introduce a new method of algebraization of logics based on multialgebras and swap structures that is similar to classical algebraization method of Lindenbaum-Tarski, but more extensive because it can be applied to systems such that some operators are non-congruential. In particular, this method will be applied to a family of non-normal modal logics and to some LFIs that are not algebraizable by the very general techniques introduced by Blok and Pigozzi. We also will obtain representation theorems for some LFIs and we will prove that, within out approach, the classes of swap structures for some axiomatic extensions of mbC are a subclass of the class of swap structures for the logic mbC.Abstract prepared by Ana Claudia de Jesus Golzio.E-mail: anaclaudiagolzio@yahoo.com.brURL: http://repositorio.unicamp.br/jspui/handle/REPOSIP/322436

Paraconsistent Logic Programming in Three and Four-Valued Logics

AbstractFrom the interaction among areas such as Computer Science, Formal Logic, and Automated Deduction arises an important new subject called Logic Programming. This has been used continuously in the theoretical study and practical applications in various fields of Artificial Intelligence. After the emergence of a wide variety of non-classical logics and the understanding of the limitations presented by first-order classical logic, it became necessary to consider logic programming based on other types of reasoning in addition to classical reasoning. A type of reasoning that has been well studied is the paraconsistent, that is, the reasoning that tolerates contradictions. However, although there are many paraconsistent logics with different types of semantics, their application to logic programming is more delicate than it first appears, requiring an in-depth study of what can or cannot be transferred directly from classical first-order logic to other types of logic.Based on studies of Tarcisio Rodrigues on the foundations of Paraconsistent Logic Programming (2010) for some Logics of Formal Inconsistency (LFIs), this thesis intends to resume the research of Rodrigues and place it in the specific context of LFIs with three- and four-valued semantics. This kind of logics are interesting from the computational point of view, as presented by Luiz Silvestrini in his Ph.D. thesis entitled “A new approach to the concept of quase-truth” (2011), and by Marcelo Coniglio and Martín Figallo in the article “Hilbert-style presentations of two logics associated to tetravalent modal algebras” [Studia Logica (2012)]. Based on original techniques, this study aims to define well-founded systems of paraconsistent logic programming based on well-known logics, in contrast to the ad hoc approaches to this question found in the literature.Abstract prepared by Kleidson Êglicio Carvalho da Silva Oliveira.E-mail: kecso10@yahoo.com.brURL: http://repositorio.unicamp.br/jspui/handle/REPOSIP/322632

On Logics of Perfect Paradefinite Algebras

The present study shows how to enrich De Morgan algebras with a perfection operator that allows one to express the Boolean properties of negation-consistency and negation-determinedness. The variety of perfect paradefinite algebras thus obtained (PP-algebras) is shown to be term-equivalent to the variety of involutive Stone algebras, introduced by R. Cignoli and M. Sagastume, and more recently studied from a logical perspective by M. Figallo-L. Cant\'u and by S. Marcelino-U. Rivieccio. This equivalence plays an important role in the investigation of the 1-assertional logic and of the order-preserving logic associated to PP-algebras. The latter logic (here called PP<=) is characterized by a single 6-valued matrix and is shown to be a Logic of Formal Inconsistency and Formal Undeterminedness. We axiomatize PP<= by means of an analytic finite Hilbert-style calculus, and we present an axiomatization procedure that covers the logics corresponding to other classes of De Morgan algebras enriched by a perfection operator.

Model Theory in a Paraconsistent Environment

AbstractThe purpose of this thesis is to develop a paraconsistent Model Theory. The basis for such a theory was launched by Walter Carnielli, Marcelo Esteban Coniglio, Rodrigo Podiack, and Tarcísio Rodrigues in the article ‘On the Way to a Wider Model Theory: Completeness Theorems for First-Order Logics of Formal Inconsistency’ [The Review of Symbolic Logic, vol. 7 (2014)].Naturally, a complete theory cannot be fully developed in a single work. Indeed, the goal of this work is to show that a paraconsistent Model Theory is a sound and worthy possibility. The pursuit of this goal is divided in three tasks: The first one is to give the theory a philosophical meaning. The second one is to transpose as many results from the classical theory to the new one as possible. The third one is to show an application of the theory to practical science.The response to the first task is a Paraconsistent Reasoning System. The start point is that paraconsistency is an epistemological concept. The pursuit of a deeper understanding of the phenomenon of paraconsistency from this point of view leads to a reasoning system based on the Logics of Formal Inconsistency. Models are regarded as states of knowledge and the concept of isomorphism is reformulated so as to give raise to a new concept that preserves a portion of the whole knowledge of each state. Based on this, a notion of refinement is created which may occur from inside or from outside the state.In order to respond to the second task, two important classical results, namely the Omitting Types Theorem and Craig’s Interpolation Theorem are shown to hold in the new system and it is also shown that, if classical results in general are to hold in a paraconsistent system, then such a system should be in essence how it was developed here.Finally, the response to the third task is a proposal of what a Paraconsistent Logic Programming may be. For that, the basis for a paraconsistent PROLOG is settled in the light of the ideas developed so far.Abstract prepared by Bruno Costa Coscarelli.E-mail: brunocostacoscarelli@gmail.comURL: http://repositorio.unicamp.br/jspui/handle/REPOSIP/331697

Logics of formal inconsistency based on distributive involutive residuated lattices

Abstract The aim of this paper is to develop an algebraic and logical study of certain paraconsistent systems, from the family of the logics of formal inconsistency (LFIs), which are definable from the degree-preserving companions of logics of distributive involutive residuated lattices ($\textrm {dIRL}$s) with a consistency operator, the latter including as particular cases, Nelson logic ($\textsf {NL}$), involutive monoidal t-norm based logic ($\textsf {IMTL}$) or nilpotent minimum ($\textsf {NM}$) logic. To this end, we first algebraically study enriched dIRLs with suitable consistency operators. In fact, we consider three classes of consistency operators, leading respectively to three subquasivarieties of such expanded residuated lattices. We characterize the simple and subdirectly irreducible members of these quasivarieties, and we extend Sendlewski’s representation results for the case of Nelson lattices with consistency operators. Finally, we define and axiomatize the logics of three quasivarieties of $ \textrm {dIRL}$s and their corresponding degree-preserving companions that belong to the family of LFIs.

Corrigendum for "Truth in a logic of formal inconsistency: How classical can it get?"

Corrigendum for "Truth in a logic of formal inconsistency: How classical can it get?"

Measuring evidence: a probabilistic approach to an extension of Belnap–Dunn logic

This paper introduces the logic of evidence and truth \({ LET}_{F}\) as an extension of the Belnap–Dunn four-valued logic \({ FDE}\). \({ LET}_{F}\) is a slightly modified version of the logic \({ LET}_{J}\), presented in Carnielli and Rodrigues (Synthese 196:3789–3813, 2017). While \({ LET}_{J}\) is equipped only with a classicality operator \({\circ }\), \({ LET}_{F}\) is equipped with a non-classicality operator \({\bullet }\) as well, dual to \({\circ }\). Both \({ LET}_{F}\) and \({ LET}_{J}\) are logics of formal inconsistency and undeterminedness in which the operator \( \circ \) recovers classical logic for propositions in its scope. Evidence is a notion weaker than truth in the sense that there may be evidence for a proposition \( \alpha \) even if \( \alpha \) is not true. As well as \({ LET}_{J}\), \({ LET}_{F}\) is able to express preservation of evidence and preservation of truth. The primary aim of this paper is to propose a probabilistic semantics for \({ LET}_{F}\) where statements \(P(\alpha )\) and \(P({\circ }\alpha )\) express, respectively, the amount of evidence available for \(\alpha \) and the degree to which the evidence for \( \alpha \) is expected to behave classically—or non-classically for \( P({\bullet }\alpha ) \). A probabilistic scenario is paracomplete when \(P(\alpha ) + P(\lnot \alpha ) < 1\), and paraconsistent when \(P(\alpha ) + P(\lnot \alpha ) > 1\), and in both cases, \(P(\circ \alpha ) < 1\). If \(P(\circ \alpha ) = 1\), or \(P({\bullet }\alpha ) = 0\), classical probability is recovered for \( \alpha \). The proposition \( {\circ }\alpha \vee {\bullet }\alpha \), a theorem of \({ LET}_{F}\), partitions what we call the information space, and thus allows us to obtain some new versions of known results of standard probability theory.

О подлинно паранепротиворечивых и подлинно параполных многозначных логиках

Статья посвящена анализу нескольких классов паранепротиворечивых и параполных логик на примере трехзначных и четырехзначных логик, сохраняющих классические истинностные значения. Результаты, представленные в статье, можно разделить на три группы. &#x0D; Первая группа результатов касается паранепротиворечивых логик. Показано, что все трехзначные подлинно паранепротиворечивые логики являются логиками формальной противоречивости, а все трехзначные логики формальной противоречивости, расширяющие позитивный фрагмент классической логики, являются языковыми вариантами подлинно паранепротиворечивых логик. Приводятся примеры четырехзначных подлинно паранепротиворечивых логик, которые не являются логиками формальной противоречивости. Найден ряд необходимых условий, которым должны соответствовать четырехзначные матрицы подлинно паранепротиворечивых логик, чтобы задаваемые этими матрицами логики не являлись логиками формальной противоречивости. Вторая группа результатов касается параполных логик. Показано, что все трехзначные подлинно параполные логики являются логиками формальной неопределенности, а все трехзначные логики формальной неопределенности, расширяющие дуально-позитивный фрагмент классической логики, являются языковыми вариантами подлинно параполных логик. Приводятся примеры четырехзначных подлинно параполных логик, которые не являются логиками формальной неопределенности. Найден ряд необходимых условий, которым должны соответствовать четырехзначные матрицы подлинно параполных логик, чтобы задаваемые этими матрицами логики не являлись логиками формальной неопределенности. Третья группа результатов касается паранормальных логик. Приводится ряд необходимых условий, которым должны соответствовать четырехзначные матрицы подлинно паранормальных логик, чтобы они не являлись ни логиками формальной противоречивости, ни логиками формальной неопределенности. Для паранормальных расширений Белнапа даются также необходимые и достаточные условия, для того чтобы они были максимальными подлинно паранормальными логиками и в то же время не являлись ни логиками формальной противоречивости, ни логиками формальной неопределенности.&#x0D; &#x0D;

SOME MODEL-THEORETIC RESULTS ON THE 3-VALUED PARACONSISTENT FIRST-ORDER LOGIC QCIORE

AbstractThe 3-valued paraconsistent logic Ciore was developed by Carnielli, Marcos and de Amo under the name LFI2, in the study of inconsistent databases from the point of view of logics of formal inconsistency (LFIs). They also considered a first-order version of Ciore called LFI2*. The logic Ciore enjoys extreme features concerning propagation and retropropagation of the consistency operator: a formula is consistent if and only if some of its subformulas is consistent. In addition, Ciore is algebraizable in the sense of Blok and Pigozzi. On the other hand, the logic LFI2* satisfies a somewhat counter-intuitive property: the universal and the existential quantifier are inter-definable by means of the paraconsistent negation, as it happens in classical first-order logic with respect to the classical negation. This feature seems to be unnatural, given that both quantifiers have the classical meaning in LFI2*, and that this logic does not satisfy the De Morgan laws with respect to its paraconsistent negation. The first goal of the present article is to introduce a first-order version of Ciore (which we call QCiore) preserving the spirit of Ciore, that is, without introducing unexpected relationships between the quantifiers. The second goal of the article is to adapt to QCiore the partial structures semantics for the first-order paraconsistent logic LPT1 introduced by Coniglio and Silvestrini, which generalizes the semantic notion of quasi-truth considered by Mikeberg, da Costa and Chuaqui. Finally, some important results of classical Model Theory are obtained for this logic, such as Robinson’s joint consistency theorem, amalgamation and interpolation. Although we focus on QCiore, this framework can be adapted to other 3-valued first-order LFIs.

Volume I: Recovery operators in logics of formal inconsistency

Fil: Barrio, Eduardo Alejandro. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Instituto de Investigaciones Filosoficas. - Sociedad Argentina de Analisis Filosofico. Instituto de Investigaciones Filosoficas; Argentina

Volume II: New advances in Logics of Formal Inconsistency

Volume II: New advances in Logics of Formal Inconsistency

Recovery operators, paraconsistency and duality

Abstract There are two foundational, but not fully developed, ideas in paraconsistency, namely, the duality between paraconsistent and intuitionistic paradigms, and the introduction of logical operators that express metalogical notions in the object language. The aim of this paper is to show how these two ideas can be adequately accomplished by the logics of formal inconsistency (LFIs) and by the logics of formal undeterminedness (LFUs). LFIs recover the validity of the principle of explosion in a paraconsistent scenario, while LFUs recover the validity of the principle of excluded middle in a paracomplete scenario. We introduce definitions of duality between inference rules and connectives that allow comparing rules and connectives that belong to different logics. Two formal systems are studied, the logics mbC and mbD, that display the duality between paraconsistency and paracompleteness as a duality between inference rules added to a common core—in the case studied here, this common core is classical positive propositional logic. The logics mbC and mbD are equipped with recovery operators that restore classical logic for, respectively, consistent and determined propositions. These two logics are then combined obtaining a pair of LFI and undeterminedness, namely, mbCD and mbCDE. The logic mbCDE exhibits some nice duality properties. Besides, it is simultaneously paraconsistent and paracomplete, and able to recover the principles of excluded middle and explosion one at a time. The last sections offer an algebraic account for such logics by adapting the swap structures semantics framework of the LFIs the LFUs. This semantics highlights some subtle aspects of these logics, and allows us to prove decidability by means of finite nondeterministic matrices.

Swap structures semantics for Ivlev-like modal logics

In 1988, J. Ivlev proposed some (non-normal) modal systems which are semantically characterized by four-valued non-deterministic matrices in the sense of A. Avron and I. Lev. Swap structures are multialgebras (a.k.a. hyperalgebras) of a special kind, which were introduced in 2016 by W. Carnielli and M. Coniglio in order to give a non-deterministic semantical account for several paraconsistent logics known as logics of formal inconsistency, which are not algebraizable by means of the standard techniques. Each swap structure induces naturally a non-deterministic matrix. The aim of this paper is to obtain a swap structures semantics for some Ivlev-like modal systems proposed in 2015 by M. Coniglio, L. Farinas del Cerro and N. Peron. Completeness results will be stated by means of the notion of Lindenbaum–Tarski swap structures, which constitute a natural generalization to multialgebras of the concept of Lindenbaum–Tarski algebras.

TWO-VALUED WEAK KLEENE LOGICS

Abstract In the literature, Weak Kleene logics are usually taken as three-valued logics. However, Suszko has challenged the main idea of many-valued logic claiming that every logic can be presented in a two-valued fashion. In this paper, we provide two-valued semantics for the Weak Kleene logics and for a number of four-valued subsystems of them. We do the same for the so-called Logics of Nonsense, which are extensions of the Weak Kleene logics with unary operators that allow looking at them as Logics of Formal Inconsistency (LFIs) and Logics of Formal Underterminedness (LFUs). Our aim with this work, rather than arguing for Suszko’s thesis, is to show that two-valued presentations of these peculiar logics enlighten the non-standard behavior of their logical connectives. More specifically, the two-valued presentations of paraconsistent logics illustrate and clarify the disjunctive flavor of the conjunction, and dually, the two-valued presentations of paracomplete subsystems of Weak Kleene logics reveal the conjunctive flavor of the disjunction.

From logics of formal inconsistency to logics of formal classicality

Abstract One of the oldest systems of paraconsistent logic is the set of so-called C-systems of Newton da Costa, and this has been generalized into a family of systems now known as logics of formal inconsistencies by Walter Carnielli, Marcelo Coniglio and João Marcos. The characteristic notion in these systems is the so-called consistency operator which, roughly speaking, indicates how gluts are behaving. One natural question then is to ask if we can let not only gluts but also gaps be around and generalize the notion of consistency into classicality. This is already considered by Andréa Loparić and da Costa in the style of C-systems. The aim of this paper is to develop a family of systems that generalizes the system of Loparić and da Costa which may be called logics of formal classicality.