Floris Bex

FLAP Journal 2025 Journal Article

Computational Models of Legal Argument

• Trevor Bench-Capon
• Katie Atkinson
• Floris Bex
• Henry Prakken
• Bart Verheij

This article reviews work on applications of argumentation-based dialogue. It takes both a broad view of dialogue and a broad view of what constitutes an application. It considers the full range of software tools that would be needed in constructing a software system that is capable of engaging in argumentation- based dialogue, along with complete applications, and includes both work that builds on formal models of dialogue, and that is more inspired by recent work on chatbots from natural language processing.

AILAW Journal 2024 Journal Article

Precedent-based reasoning with incomplete information for human-in-the-loop decision support

• Daphne Odekerken
• Floris Bex
• Henry Prakken

Abstract We define and study the notions of stability and relevance for precedent-based reasoning, focusing on Horty’s result model of precedential constraint. According to this model, precedents constrain the possible outcomes for a focus case, which is a yet undecided case, where precedents and the focus case are compared on their characteristics (called dimensions). In this paper, we refer to the enforced outcome for the focus case as its justification status. In contrast to earlier work, we do not assume that all dimension values of the focus case or the precedent cases have been established with certainty: rather, each dimension is assigned a set of possible values. We define a focus case as stable if its justification status is the same for every choice of the possible values. For focus cases that are not stable, we study the task of identifying relevance: which possible values should be excluded to make the focus case stable? In addition, we introduce the notion of possibility to verify if a user can assign an outcome to an unstable focus case without making the case base of precedents inconsistent. We show how the tasks of identifying justification, stability, relevance and possibility can be applied for human-in-the-loop decision support. Finally, we discuss the computational complexity of these tasks and provide efficient algorithms.

KR Conference 2023 Conference Paper

ORLA: Learning Explainable Argumentation Models

• Cándido Otero
• Dennis Craandijk
• Floris Bex

This paper presents ORLA (Online Reinforcement Learning Argumentation), a new approach for learning explainable symbolic argumentation models through direct exploration of the world. ORLA takes a set of expert arguments that promote some action in the world, and uses reinforcement learning to determine which of those arguments are the most effective for performing a task by maximizing a performance score. Thus, ORLA learns a preference ranking over the expert arguments such that the resulting value-based argumentation framework (VAF) can be used as a reasoning engine to select actions for performing the task. Although model-extraction methods exist that extract a VAF by mimicking the behavior of some non-symbolic model (e. g. , a neural network), these extracted models are only approximations to their non-symbolic counterparts, which may result in both a performance loss and non-faithful explanations. Conversely, ORLA learns a VAF through direct interaction with the world (online learning), thus producing faithful explanations without sacrificing performance. This paper uses the Keepaway world as a case study and shows that models trained using ORLA not only perform better than those extracted from non-symbolic models but are also more robust. Moreover, ORLA is evaluated as a strategy discovery tool, finding a better solution than the expert strategy proposed by a related study.

AAMAS Conference 2022 Conference Paper

Contrastive Explanations for Argumentation-Based Conclusions

• Annemarie Borg
• Floris Bex

In this paper we discuss contrastive explanations for formal argumentation – the question why one argument (the fact) can be accepted, whilst another argument (the foil) cannot be accepted. We show under which conditions contrastive explanations in abstract argumentation are meaningful, and how argumentation allows us to make implicit foils explicit.

AILAW Journal 2022 Journal Article

Correction: thirty years of Artificial Intelligence and Law: the second decade

• Giovanni Sartor
• Michał Araszkiewicz
• Katie Atkinson
• Floris Bex
• Tom van Engers
• Enrico Francesconi
• Henry Prakken
• Giovanni Sileno

AAAI Conference 2022 Conference Paper

Enforcement Heuristics for Argumentation with Deep Reinforcement Learning

• Dennis Craandijk
• Floris Bex

In this paper, we present a learning-based approach to the symbolic reasoning problem of dynamic argumentation, where the knowledge about attacks between arguments is incomplete or evolving. Specifically, we employ deep reinforcement learning to learn which attack relations between arguments should be added or deleted in order to enforce the acceptability of (a set of) arguments. We show that our Graph Neural Network (GNN) architecture EGNN can learn a near optimal enforcement heuristic for all common argumentfixed enforcement problems, including problems for which no other (symbolic) solvers exist. We demonstrate that EGNN outperforms other GNN baselines and on enforcement problems with high computational complexity performs better than state-of-the-art symbolic solvers with respect to efficiency. Thus, we show our neuro-symbolic approach is able to learn heuristics without the expert knowledge of a human designer and offers a valid alternative to symbolic solvers. We publish our code at https: //github. com/DennisCraandijk/DL- Abstract-Argumentation.

AILAW Journal 2022 Journal Article

Thirty years of Artificial Intelligence and Law: the second decade

• Giovanni Sartor
• Michał Araszkiewicz
• Katie Atkinson
• Floris Bex
• Tom van Engers
• Enrico Francesconi
• Henry Prakken
• Giovanni Sileno

Abstract The first issue of Artificial Intelligence and Law journal was published in 1992. This paper provides commentaries on nine significant papers drawn from the Journal’s second decade. Four of the papers relate to reasoning with legal cases, introducing contextual considerations, predicting outcomes on the basis of natural language descriptions of the cases, comparing different ways of representing cases, and formalising precedential reasoning. One introduces a method of analysing arguments that was to become very widely used in AI and Law, namely argumentation schemes. Two relate to ontologies for the representation of legal concepts and two take advantage of the increasing availability of legal corpora in this decade, to automate document summarisation and for the mining of arguments.

IS Journal 2021 Journal Article

A Basic Framework for Explanations in Argumentation

• Annemarie Borg
• Floris Bex

We discuss explanations for formal (abstract and structured) argumentation—the question of whether and why a certain argument or claim can be accepted (or not) under various extension-based semantics. We introduce a flexible framework, which can act as the basis for many different types of explanations. For example, we can have simple or comprehensive explanations in terms of arguments for or against a claim, arguments that (indirectly) defend a claim, the evidence (knowledge base) that supports or is incompatible with a claim, and so on. We show how different types of explanations can be captured in our basic framework, discuss a real-life application and formally compare our framework to existing work.

KR Conference 2021 Conference Paper

Enforcing Sets of Formulas in Structured Argumentation

• Annemarie Borg
• Floris Bex

Enforcement, adjusting an argumentation framework such that a certain set of arguments becomes acceptable, is an important research topic within the study of dynamic argumentation, but one that has been little studied for structured argumentation. In this paper we study enforcement in a general structured argumentation setting. In particular, we study conditions on the argumentation setting and the knowledge base that ensure (or prevent) the acceptability of sets of formulas for structured argumentation frameworks.

IJCAI Conference 2020 Conference Paper

Deep Learning for Abstract Argumentation Semantics

• Dennis Craandijk
• Floris Bex

In this paper, we present a learning-based approach to determining acceptance of arguments under several abstract argumentation semantics. More specifically, we propose an argumentation graph neural network (AGNN) that learns a message-passing algorithm to predict the likelihood of an argument being accepted. The experimental results demonstrate that the AGNN can almost perfectly predict the acceptability under different semantics and scales well for larger argumentation frameworks. Furthermore, analysing the behaviour of the message-passing algorithm shows that the AGNN learns to adhere to basic principles of argument semantics as identified in the literature, and can thus be trained to predict extensions under the different semantics – we show how the latter can be done for multi-extension semantics by using AGNNs to guide a basic search. We publish our code at https: //github. com/DennisCraandijk/DL-Abstract-Argumentation.

AILAW Journal 2020 Journal Article

In memoriam Douglas N. Walton: the influence of Doug Walton on AI and law

• Katie Atkinson
• Trevor Bench-Capon
• Floris Bex
• Thomas F. Gordon
• Henry Prakken
• Giovanni Sartor
• Bart Verheij

Abstract Doug Walton, who died in January 2020, was a prolific author whose work in informal logic and argumentation had a profound influence on Artificial Intelligence, including Artificial Intelligence and Law. He was also very interested in interdisciplinary work, and a frequent and generous collaborator. In this paper seven leading researchers in AI and Law, all past programme chairs of the International Conference on AI and Law who have worked with him, describe his influence on their work.

AILAW Journal 2017 Journal Article

Introduction to the special issue on Artificial Intelligence for Justice (AI4J)

• Floris Bex
• Henry Prakken
• Tom van Engers
• Bart Verheij

AILAW Journal 2012 Journal Article

Legal stories and the process of proof

• Floris Bex
• Bart Verheij

Abstract In this paper, we continue our research on a hybrid narrative-argumentative approach to evidential reasoning in the law by showing the interaction between factual reasoning (providing a proof for ‘what happened’ in a case) and legal reasoning (making a decision based on the proof). First we extend the hybrid theory by making the connection with reasoning towards legal consequences. We then emphasise the role of legal stories (as opposed to the factual stories of the hybrid theory). Legal stories provide a coherent, holistic legal perspective on a case. They steer what needs to be proven but are also selected on the basis of what can be proven. We show how these legal stories can be used to model a shift of the legal perspective on a case, and we discuss how gaps in a legal story can be filled using a factual story (i. e. the process of reasoning with circumstantial evidence). Our model is illustrated by a discussion of the Dutch Wamel murder case.

AILAW Journal 2009 Journal Article

Did he jump or was he pushed?

• Floris Bex
• Trevor Bench-Capon
• Katie Atkinson

Abstract In this paper, we present a particular role for abductive reasoning in law by applying it in the context of an argumentation scheme for practical reasoning. We present a particular scheme, based on an established scheme for practical reasoning, that can be used to reason abductively about how an agent might have acted to reach a particular scenario, and the motivations for doing so. Plausibility here depends on a satisfactory explanation of why this particular agent followed these motivations in the particular situation. The scheme is given a formal grounding in terms of action-based alternating transition systems and we illustrate the approach with a running legal example.

AILAW Journal 2005 Journal Article

Towards a multi-agent system for regulated information exchange in crime investigations

• Pieter Dijkstra
• Floris Bex
• Henry Prakken
• Kees de Vey Mestdagh

Abstract This paper outlines a multi-agent architecture for regulated information exchange of crime investigation data between police forces. Interactions between police officers about information exchange are analysed as negotiation dialogues with embedded persuasion dialogues. An architecture is then proposed consisting of two agents, a requesting agent and a responding agent, and a communication language and protocol with which these agents can interact to promote optimal information exchange while respecting the law. Finally, dialogue policies are defined for the individual agents, specifying their behaviour within a negotiation. Essentially, when deciding to accept or reject an offer or to make a counteroffer, an agent first determines whether it is obligatory or permitted to perform the actions specified in the offer. If permitted but not obligatory, the agent next determines whether it is in his interest to accept the offer.

AILAW Journal 2003 Journal Article

Towards a Formal Account of Reasoning about Evidence: Argumentation Schemes and Generalisations

• Floris Bex
• Henry Prakken
• Chris Reed
• Douglas Walton

This paper studies the modelling of legal reasoning about evidence within general theories of defeasible reasoning and argumentation. In particular, Wigmore's method for charting evidence and its use by modern legal evidence scholars is studied in order to give a formal underpinning in terms of logics for defeasible argumentation. Two notions turn out to be crucial, viz. argumentation schemes and empirical generalisations.