arXiv subjects

Meghdad Ghari

Publications and source records attributed to Meghdad Ghari.

12 recordsLinked to original sources

arXiv2025

Justification logics with counterfactual and relevant conditionals

The purpose of this paper is to introduce justification logics based on conditional logics. We introduce a new family of logics, called conditional justification logics, which incorporates a counterfactual conditional in its language. For the semantics, we offer relational models that merge the selection-function semantics of conditional logics with the relational semantics of justification logics. As an application, we formalize Nozick's counterfactual conditions in his analysis of knowledge and investigate their connection to Aumann's concepts of knowledge. Additionally, we explore Gettier's counterexamples to the justified true belief analysis, as well as McGinn's counterexamples to Nozick's analysis of knowledge. Furthermore, we introduce a justification logic that includes a relevant counterfactual conditional and we demonstrate the variable-sharing property for this conditional. We also develop a tableau system for this logic and establish its completeness with respect to Routley relational models. Finally, we formalize Nozick's counterfactual conditions using this relevant counterfactual conditional and represent the sheep in the field example of Chisholm within this logic.

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arXiv2023

Impossible and Conflicting Obligations in Justification Logic

Different notions of the consistency of obligations collapse in standard deontic logic. In justification logics, which feature explicit reasons for obligations, the situation is different. Their strength depends on a constant specification and on the available set of operations for combining different reasons. We present different consistency principles in justification logic and compare their logical strength. We propose a novel semantics for which justification logics with the explicit version of axiom D, jd, are complete for arbitrary constant specifications. We then discuss the philosophical implications with regard to some deontic paradoxes.

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arXiv2021

A temporal logic of epistemic and normative justifications, with an application to the Protagoras paradox

We combine linear temporal logic (with both past and future modalities) with a deontic version of justification logic to provide a framework for reasoning about time and epistemic and normative reasons. In addition to temporal modalities, the resulting logic contains two kinds of justification assertions: epistemic justification assertions and deontic justification assertions. The former presents justification for the agent's knowledge and the latter gives reasons for why a proposition is obligatory. We present two kinds of semantics for the logic: one based on Fitting models and the other based on neighborhood models. The use of neighborhood semantics enables us to define the dual of deontic justification assertions properly, which corresponds to the notion of permission in deontic logic. We then establish the soundness and completeness of an axiom system of the logic with respect to these semantics. Further, we formalize the Protagoras versus Euathlus paradox in this logic and present a precise analysis of the paradox, and also briefly discuss Leibniz's solution.

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arXiv2021

Algebraic Semantics for the Logic of Proofs

We present algebraic semantics for the classical logic of proofs based on Boolean algebras. We also extend the language of the logic of proofs in order to have a Boolean structure on justification terms and equality predicate on terms. In the end, the completeness theorem and certain generalizations of Stone's representation theorem are obtained for all proposed algebras.

math.LO↗

arXiv2018

Linear Temporal Justification Logics with Past Operators

In this paper we present various temporal justification logics involving both past and future time modalities. We combine Artemov's logic of proofs with linear temporal logic (with both past and future operators), and establish its soundness and completeness. Then we investigate several principles describing the interaction of justification and time.

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arXiv2017

Temporal Justification Logic

Justification logics are modal-like logics with the additional capability of recording the reason, or justification, for modalities in syntactic structures, called justification terms. Justification logics can be seen as explicit counterparts to modal logics. The behavior and interaction of agents in distributed system is often modeled using logics of knowledge and time. In this paper, we sketch some preliminary ideas on how the modal knowledge part of such logics of knowledge and time could be replaced with an appropriate justification logic.

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arXiv2016

Analytic Tableaux for Justification Logics

In this paper we present analytic tableau proof systems for various justification logics. We show that the tableau systems are sound and complete with respect to Mkrtychev models. In order to prove the completeness of the tableaux, we give a syntactic proof of cut elimination. We also show the subformula property for our tableaux, and prove the decidability of justification logics for finite constant specifications.

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arXiv2016

Tableaux for First Order Logic of Proofs

In this paper we present a tableau proof system for first order logic of proofs FOLP. We show that the tableau system is sound and complete with respect to Mkrtychev models of FOLP.

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arXiv2015

A Note on Fixed Points in Justification Logics and the Surprise Test Paradox

In this note we study the effect of adding fixed points to justification logics. We introduce two extensions of justification logics: extensions by fixed point (or diagonal) operators, and extensions by least fixed points. The former is a justification version of Smorynski's Diagonalization Operator Logic, and the latter is a justification version of Kozen's modal $μ$-calculus. We also introduce fixed point extensions of Fitting's quantified logic of proofs, and formalize the Knower Paradox and the Surprise Test Paradox in these extensions. By interpreting a surprise statement as a statement for which there is no justification, we give a solution to the self-reference version of the Surprise Test Paradox in quantified logic of proofs. We also give formalizations of the Surprise Test Paradox in timed modal epistemic logics, and in Gödel-Löb provability logic.

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arXiv2014

Justification Logics in a Fuzzy Setting

Justification Logics provide a framework for reasoning about justifications and evidences. Most of the accounts of justification logics are crisp in the sense that agent's justifications for a statement is convincing or is not. In this paper, we study fuzzy variants of justification logics, in which an agent can have a justification for a statement with a certainty degree between 0 and 1. We replaced the classical base of the justification logics with some known fuzzy logics: Hajek's basic logic, {\L}ukasiewicz logic, G\"odel logic, product logic, and rational Pavelka logic. In all of the resulting systems we introduced fuzzy models (fuzzy possible world semantics with crisp accessibility relation) for our systems, and established the soundness theorems. In the extension of rational Pavelka logic we also proved a graded-style completeness theorem.

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arXiv2014

Tableau Proof Systems for Justification Logics

In this paper we present tableau proof systems for various justification logics. We show that the tableau systems are sound and complete with respect to Mkrtychev models. In order to prove the completeness of the tableaux, we give a syntactic proof of cut elimination. We also show the subformula property for our tableaux.

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arXiv2014

Labeled Sequent Calculus and Countermodel Construction for Justification Logics

Justification logics are modal-like logics that provide a framework for reasoning about justifications. This paper introduces labeled sequent calculi for justification logics, as well as for hybrid modal-justification logics. Using the method due to Sara Negri, we internalize the Kripke-style semantics of justification logics, known as Fitting models, within the syntax of the sequent calculus to produce labeled sequent calculus. We show that our labeled sequent calculi enjoy a weak subformula property, all of the rules are invertible and the structural rules (weakening and contraction) and cut are admissible. Finally soundness and completeness are established, and termination of proof search for some of the labeled systems are shown. We describe a procedure, for some of the labeled systems, which produces a derivation for valid sequents and a countermodel for non-valid sequents. We also show a model correspondence for justification logics in the context of labeled sequent calculus.

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