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See detailNon-Admissibility in abstract argumentation
Dvorak, Wolfgang; Rienstra, Tjitze; van der Torre, Leon UL et al

in Frontiers in Artificial Intelligence and Applications (2022), 353

In this paper, we give an overview of several recent proposals for non-Admissible non-naive semantics for abstract argumentation frameworks. We highlight the similarities and differences between weak ... [more ▼]

In this paper, we give an overview of several recent proposals for non-Admissible non-naive semantics for abstract argumentation frameworks. We highlight the similarities and differences between weak admissibility-based approaches and undecidedness-blocking approaches using examples and principles as well as a study of their computational complexity. We introduce a kind of strengthened undecidedness-blocking semantics combining some of the distinctive behaviours of weak admissibility-based semantics with the lower complexity of undecidedness-blocking approaches. We call it loop semantics, because in our new semantics, an argument can only be undecided if it is part of a loop of undecided arguments. Our paper shows how a principle-based approach and a complexity-based approach can be used in tandem to further develop the foundations of formal argumentation. [less ▲]

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See detailMulti-agent Argumentation and Dialogue
Arisaka, Ryuta; Dauphin, Jérémie UL; Satoh, Ken et al

in Journal of Applied Logics (2022), 9(4), 853-886

In this chapter we give an overview of multi-agent abstract argumentation and dialogue, and its application to formalise legal reasoning. The basis of multi-agent abstract argumentation is input/output ... [more ▼]

In this chapter we give an overview of multi-agent abstract argumentation and dialogue, and its application to formalise legal reasoning. The basis of multi-agent abstract argumentation is input/output argumentation studied by Baroni et al., distinguishing between the individual acceptance of agents and the collective acceptance of the system. The former may also be seen as a kind of conditional reasoning, and the latter may be seen as the reasoning of an external observer. We extend input/output argumentation in two ways. First, we introduce epistemic trust and agent communication, where the former is based on a social network representing epistemic trust, and the latter is based on so-called sub-framework semantics. Second, we introduce dialogue semantics for abstract argumentation by refining agent communication into dialogue steps. A dialogue is a sequence of steps from the framework to the extensions, where in each step of the sequence an agent can commit to accepting some arguments, or commit to hide or reveal one of his rejected arguments. The revealed arguments are then aggregated and an external observer, in our example a judge, can compute which arguments are finally acceptable at a global level. [less ▲]

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See detailDefeasible Deontic Logic: Arguing about Permission and Obligation
Dong, Huimin; Liao, Beishui; Markovich, Réka UL et al

in Journal of Applied Logics (2022), 9(4), 957-1018

Defeasible deontic logic uses techniques from non-monotonic logic to address various challenges in normative reasoning, such as prima facie permissions and obligations, moral dilemmas, deontic detachment ... [more ▼]

Defeasible deontic logic uses techniques from non-monotonic logic to address various challenges in normative reasoning, such as prima facie permissions and obligations, moral dilemmas, deontic detachment, contrary-to-duty reasoning and legal interpretation. In this article, we use formal argumentation to design defeasible deontic logics, based on two classical deontic logics. In particular, we use the ASPIC+ structured argumentation theory to define non-monotonic variants of well-understood monotonic modal logics. We illustrate the ASPIC+-based approach and the resulting defeasible deontic logics using argumentation about strong permission. [less ▲]

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See detailReasoning on conflicting information: An empirical study of Formal Argumentation
Guillaume, Mathieu UL; Cramer, Marcos UL; van der Torre, Leon UL et al

in PLoS ONE (2022), 17(8 August),

According to the Argumentative Theory, human reasoning has an argumentative function, which consists of devising and evaluating arguments for and against various claims. It is however unclear how humans ... [more ▼]

According to the Argumentative Theory, human reasoning has an argumentative function, which consists of devising and evaluating arguments for and against various claims. It is however unclear how humans handle conflicting claims they face in everyday life (i.e., “Bob is telling me that Alice is at the library” vs. “Charles is telling me that Alice is at home”). We here investigate human argumentative reasoning in the light of Formal Argumentation, a research field that develops formal methods to give a normative account of argumentation and reasoning about conflicting information. In Formal Argumentation, multiple argumentation semantics that allow selecting sets of jointly acceptable arguments have been proposed. Nonetheless, it is unclear which of these semantics predicts best how humans evaluate the acceptability of conflicting arguments. We conducted an empirical study in which 130 young adults judged natural language arguments. We instructed them to draw the attack relation between the given arguments and to evaluate the acceptability of each of these arguments. Our results show that human judgments on the existence and directionality of attacks between the arguments conform to theoretical predictions from Formal Argumentation. We further found out that some less well-known argumentation semantics predicted human evaluation better than the most well-known semantics. These findings support the cognitive plausibility of variants of Formal Argumentation and bring new insights into reasoning about conflicting information. [less ▲]

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See detailNormative Change: An AGM Approach
Maranhão, Juliano; Casini, Giovanni; Pigozzi, Gabriella et al

in Journal of Applied Logics (2022), 9(4), 787-852

Studying normative change has practical and theoretical interests. Changing legal rules poses interpretation problems to determine the content of legal rules. The question of interpretation is tightly ... [more ▼]

Studying normative change has practical and theoretical interests. Changing legal rules poses interpretation problems to determine the content of legal rules. The question of interpretation is tightly linked to those of determining the validity and the ability to produce effects of legal rules. Different formal models of normative change seem better suited to capture these dimensions: the dimension of validity appears to be better captured by the AGM approach, whereas syntactic methods are better suited to model how rules’ effects are blocked or enabled. Historically, the AGM approach of belief revision (on which we focus in this chapter) was the first formal model of normative change. We provide a survey on the AGM approach along with the main criticisms made to it. We then turn to a formal analysis of normative change that combines AGM theory and input/output logic, allowing for a clear distinction between norms and obligations. Our approach addresses some of the difficulties of normative change, like the combination of constitutive and regulative rules (and the normative conflicts that may arise from such a combination), the revision and contraction of normative systems, as well as the contraction of normative systems that combine sets of constitutive and regulative rules. We end our chapter by highlighting and discussing some challenges and open problems of normative change in the AGM approach. [less ▲]

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See detailNew-Generation AIs Reasoning about Norms and Values
Markovich, Réka UL; Najjar, Amro UL; van der Torre, Leon UL

in Logics for New-Generation AI 2021 (2021)

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See detailNew Weak Admissibility Semantics for Abstract Argumentation
Dauphin, Jérémie UL; Rienstra, Tjitze; van der Torre, Leon UL

in International Conference on Logic and Argumentation (2021)

Baumann, Brewka and Ulbricht recently introduced weak admissibility as an alternative to Dung’s notion of admissibility, and they used it to define weakly preferred, weakly complete and weakly grounded ... [more ▼]

Baumann, Brewka and Ulbricht recently introduced weak admissibility as an alternative to Dung’s notion of admissibility, and they used it to define weakly preferred, weakly complete and weakly grounded semantics of argumentation frameworks. In earlier work, we introduced two variants of their new semantics which we called qualified and semi-qualified semantics. We analysed all known variants of weak admissibility semantics with respect to some of the principles discussed in the literature on abstract argumentation, as well as some new principles we introduced to distinguish them all. Such a principle-based analysis can be used not only for selecting a semantics for an application, or for algorithmic design, but also for further research into weak admissibility semantics. In this paper, we introduce six new kinds of semantics based on weak admissibility, and we provide an initial principle-based analysis. The analysis illustrates various ways in which the new semantics improve on existing ones. [less ▲]

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See detailExpectation: Personalized Explainable Artificial Intelligence for Decentralized Agents with Heterogeneous Knowledge
Calvaresi, Davide; Ciatto, Giovanni; Najjar, Amro UL et al

in Calvaresi, Davide; Najjar, Amro; Winikoff, Michael (Eds.) et al Explainable and Transparent AI and Multi-Agent Systems - Third International Workshop, EXTRAAMAS 2021, Virtual Event, May 3-7, 2021, Revised Selected Papers (2021)

Explainable AI (XAI) has emerged in recent years as a set of techniques and methodologies to interpret and explain machine learning (ML) predictors. To date, many initiatives have been proposed ... [more ▼]

Explainable AI (XAI) has emerged in recent years as a set of techniques and methodologies to interpret and explain machine learning (ML) predictors. To date, many initiatives have been proposed. Nevertheless, current research efforts mainly focus on methods tailored to specific ML tasks and algorithms, such as image classification and sentiment analysis. However, explanation techniques are still embryotic, and they mainly target ML experts rather than heterogeneous end-users. Furthermore, existing solutions assume data to be centralised, homogeneous, and fully/continuously accessible—circumstances seldom found altogether in practice. Arguably, a system-wide perspective is currently missing. The project named “Personalized Explainable Artificial Intelligence for Decentralized Agents with Heterogeneous Knowledge” (Expectation) aims at overcoming such limitations. This manuscript presents the overall objectives and approach of the Expectation project, focusing on the theoretical and practical advance of the state of the art of XAI towards the construction of personalised explanations in spite of decentralisation and heterogeneity of knowledge, agents, and explainees (both humans or virtual). To tackle the challenges posed by personalisation, decentralisation, and heterogeneity, the project fruitfully combines abstractions, methods, and approaches from the multi-agent systems, knowledge extraction / injec- tion, negotiation, argumentation, and symbolic reasoning communities. [less ▲]

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See detailA Principle-based Analysis of Abstract Agent Argumentation Semantics
Yu, Liuwen UL; Chen, Dongheng; Qiao, Lisha et al

in Bienvenu, Meghyn; Lakemeyer, Gerhard; Erdem, Esra (Eds.) Proceedings of the 18th International Conference on Principles of Knowledge Representation and Reasoning, KR 2021, Online event, November 3-12, 2021 (2021)

Abstract agent argumentation frameworks extend Dung’s theory with agents, and in this paper we study four types of semantics for them. First, agent defense semantics replaces Dung’s notion of defense by ... [more ▼]

Abstract agent argumentation frameworks extend Dung’s theory with agents, and in this paper we study four types of semantics for them. First, agent defense semantics replaces Dung’s notion of defense by some kind of agent defense. Second, social agent semantics prefers arguments that belong to more agents. Third, agent reduction semantics considers the perspective of individual agents. Fourth, agent filtering semantics are inspired by a lack of knowledge. We study five existing principles and we introduce twelve new ones. In total, we provide a full analysis of fifty-two agent semantics and the seventeen principles. [less ▲]

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See detailTowards AI Logic for Social Reasoning
Dong, Huimin; Markovich, Réka UL; van der Torre, Leon UL

E-print/Working paper (2021)

Artificial Intelligence (AI) logic formalizes the reasoning of intelligent agents. In this paper, we discuss how an argumentation-based AI logic could be used also to formalize important aspects of social ... [more ▼]

Artificial Intelligence (AI) logic formalizes the reasoning of intelligent agents. In this paper, we discuss how an argumentation-based AI logic could be used also to formalize important aspects of social reasoning. Besides reasoning about the knowledge and actions of individual agents, social AI logic can reason also about social dependencies among agents using the rights, obligations and permissions of the agents. We discuss four aspects of social AI logic. First, we discuss how rights represent relations between the obligations and permissions of intelligent agents. Second, we discuss how to argue about the right-to-know, a central issue in the recent discussion of privacy and ethics. Third, we discuss how a wide variety of conflicts among intelligent agents can be identified and (sometimes) resolved by comparing formal arguments. Importantly, to cover a wide range of arguments occurring in daily life, also fallacious arguments can be represented and reasoned about. Fourth, we discuss how to argue about the freedom to act for intelligent agents. Examples from social, legal and ethical reasoning highlight the challenges in developing social AI logic. The discussion of the four challenges leads to a research program for argumentation-based social AI logic, contributing towards the future development of AI logic. [less ▲]

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See detailBase Argumentation as an Abstraction of Deductive Argumentation
Chen, Jinsheng; Liao, Beishui; van der Torre, Leon UL

in Baroni, Pietro; Benzmüller, Christoph; Wáng, Yì N. (Eds.) Logic and Argumentation - 4th International Conference, CLAR 2021, Hangzhou, China, October 20-22, 2021, Proceedings (2021)

Base argumentation is a logic-based instantiation of abstract argumentation. Each base argument is a subset of the given knowledge base. In this paper, we show that base argumentation satisfies some ... [more ▼]

Base argumentation is a logic-based instantiation of abstract argumentation. Each base argument is a subset of the given knowledge base. In this paper, we show that base argumentation satisfies some rationality postulates, and that base argumentation is equivalent to deductive argumentation under complete semantics. Due to its simplicity, base argumentation can be seen as an abstraction of deductive argumentation. [less ▲]

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See detailPopulating legal ontologies using semantic role labeling
Humpreys, Lilo; Boella, Guido; van der Torre, Leon UL et al

in Artificial Intelligence and Law (2021), 29(2), 171-211

This article seeks to address the problem of the ‘resource consumption bottleneck’ of creating legal semantic technologies manually. It describes a semantic role labeling based information extraction ... [more ▼]

This article seeks to address the problem of the ‘resource consumption bottleneck’ of creating legal semantic technologies manually. It describes a semantic role labeling based information extraction system to extract definitions and norms from legislation and represent them as structured norms in legal ontologies. The output is intended to help make laws more accessible, understandable, and searchable in a legal document management system. [less ▲]

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See detailArguing coalitions in abstract argumentation
Qiao, Lisha; Shen, Yiqi; Yu, Liuwen et al

in Liao, Beishui; Luo, Jieting; van der Torre, Leon (Eds.) Logics for New-Generation AI 2021 (2021)

In this paper, we are interested in different ways in which agents can collaborate in abstract agent argumentation. First, if arguments are accepted when they are put forward by more than one agent, then ... [more ▼]

In this paper, we are interested in different ways in which agents can collaborate in abstract agent argumentation. First, if arguments are accepted when they are put forward by more than one agent, then agents can put forward arguments from other agents of the coalition. Second, agents can put forward arguments to defend argu- ments from other agents of the coalition. For example, in expert opinion, a domain expert can put forward an argument defending an argument made by a politician, even when the politician cannot judge the correctness of the argument. Third, agents from a coalition can collectively defend an argument they share, without being able to defend the argument individually. In this paper, we formalize the different kinds of collaboration in abstract agent argumentation, and we illustrate the coalition for- mation with a case study in political debate. [less ▲]

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See detailInterpretations of Support Among Arguments
Yu, Liuwen UL; Markovich, Réka UL; van der Torre, Leon UL

in Proceedings of the 33rd International Conference on Legal Knowledge and Information Systems (JURIX 2020) (2020, December)

The theory of formal argumentation distinguishes and unifies various notions of attack, support and preference among arguments, and principles are used to classify the semantics of various kinds of ... [more ▼]

The theory of formal argumentation distinguishes and unifies various notions of attack, support and preference among arguments, and principles are used to classify the semantics of various kinds of argumentation frameworks. In this paper, we consider the case in which we know that an argument is supporting another one, but we do not know yet which kind of support it is. Most common in the literature is to classify support as deductive, necessary, or evidentiary. Alternatively, support is characterized using principles. We discuss the interpretation of support using a legal divorce action. Technical results and proofs can be found in an accompanying technical report. [less ▲]

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See detailLogiKEy Workbench: Deontic Logics, Logic Combinations and Expressive Ethical and Legal Reasoning (Isabelle/HOL Dataset)
Benzmüller, Christoph UL; Farjami, Ali UL; Fuenmajor, David et al

in Data in Brief (2020), 33

The LogiKEy workbench and dataset for ethical and legal reasoning is presented. This workbench simultaneously supports development, experimentation, assessment and deployment of formal logics and ethical ... [more ▼]

The LogiKEy workbench and dataset for ethical and legal reasoning is presented. This workbench simultaneously supports development, experimentation, assessment and deployment of formal logics and ethical and legal theories at different conceptual layers. More concretely, it comprises, in form of a dataset (Isabelle/HOL theory files), formal encodings of multiple deontic logics, logic combinations, deontic paradoxes and normative theories in the higher-order proof assistant system Isabelle/HOL. The data were acquired through application of the LogiKEy methodology, which supports experimentation with different normative theories, in different application scenarios, and which is not tied to specific logics or logic combinations. Our workbench consolidates related research contributions of the authors and it may serve as a starting point for further studies and experiments in flexible and expressive ethical and legal reasoning. It may also support hands-on teaching of non-trivial logic formalisms in lecture courses and tutorials. [less ▲]

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See detailDesigning normative theories for ethical and legal reasoning: LogiKEy framework, methodology, and tool support
Benzmüller, Christoph; Parent, Xavier; van der Torre, Leon UL

in Artificial Intelligence and Law (2020), 287

A framework and methodology|termed LogiKEy|for the design and engineering of ethical reasoners, normative theories and deontic logics is presented. The overall motivation is the development of suitable ... [more ▼]

A framework and methodology|termed LogiKEy|for the design and engineering of ethical reasoners, normative theories and deontic logics is presented. The overall motivation is the development of suitable means for the control and governance of intelligent autonomous systems. LogiKEy's unifying formal framework is based on semantical embeddings of deontic logics, logic combinations and ethico-legal domain theories in expressive classic higher-order logic (HOL). This meta-logical approach enables the provision of powerful tool support in LogiKEy: off-the-shelf theorem provers and model finders for HOL are assisting the LogiKEy designer of ethical intelligent agents to flexibly experiment with underlying logics and their combinations, with ethico-legal domain theories, and with concrete examples|all at the same time. Continuous improvements of these off-the-shelf provers, without further ado, leverage the reasoning performance in LogiKEy. Case studies, in which the LogiKEy framework and methodology has been applied and tested, give evidence that HOL's undecidability often does not hinder e fficient experimentation. [less ▲]

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See detailArtificial Intelligence in Space
Long, George Anthony; Santos, Cristiana; Rapp, Lucien et al

E-print/Working paper (2020)

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See detailA bimodal simulation of defeasibility in thenormative domain
Libal, Tomer UL; van der Torre, Leon UL; Gabbay, Dov M. UL et al

in CEUR Workshop Proceedings (2020)

In the present work we illustrate how two sorts of defeasiblereasoning that are fundamental in the normative domain, that is, reasoning about exceptions and reasoning about violations, can be simulated ... [more ▼]

In the present work we illustrate how two sorts of defeasiblereasoning that are fundamental in the normative domain, that is, reasoning about exceptions and reasoning about violations, can be simulated via monotonic propositional theories based on a bimodal language with primitive operators representing knowledge and obligation. The proposed theoretical framework paves the way to using native theorem provers for multimodal logic, such as MleanCoP, in order to automate normative reasoning. [less ▲]

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See detailIntention as commitment toward time
van Zee, Marc; Doder, Dragan; van der Torre, Leon UL et al

in Artificial Intelligence and Law (2020), 283

In this paper we address the interplay among intention, time, and belief in dynamic environments. The first contribution is a logic for reasoning about intention, time and belief, in which assumptions of ... [more ▼]

In this paper we address the interplay among intention, time, and belief in dynamic environments. The first contribution is a logic for reasoning about intention, time and belief, in which assumptions of intentions are represented by preconditions of intended actions. Intentions and beliefs are coherent as long as these assumptions are not violated, i.e. as long as intended actions can be performed such that their preconditions hold as well. The second contribution is the formalization of what-if scenarios: what happens with intentions and beliefs if a new (possibly conflicting) intention is adopted, or a new fact is learned? An agent is committed to its intended actions as long as its belief-intention database is coherent. We conceptualize intention as commitment toward time and we develop AGM-based postulates for the iterated revision of belief-intention databases, and we prove a Katsuno-Mendelzon-style representation theorem. [less ▲]

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See detailInterpretation of Support among Arguments
Yu, Liuwen; Markovich, Réka UL; van der Torre, Leon UL

in Legal Knowledge and Information Systems – Frontiers in Artificial Intelligence and Application Series (2020)

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