Henry Prakken

AAAI Conference 2026 Conference Paper

A Fortiori Case-Based Reasoning: From Theory to Data (Abstract Reprint)

• Wijnand van Woerkom
• Davide Grossi
• Henry Prakken
• Bart Verheij

The widespread application of uninterpretable machine learning systems for sensitive purposes has spurred research into elucidating the decision-making process of these systems. These efforts have their background in many different disciplines, one of which is the field of AI & law. In particular, recent works have observed that machine learning training data can be interpreted as legal cases. Under this interpretation, the formalism developed to study case law, called the theory of precedential constraint, can be used to analyze the way in which machine learning systems draw on training data—or should draw on them—to make decisions. In the present work, we advance the theory underlying these explanation methods, by relating it to order theory and logic. This allows us to write a software implementation of the theory that can be used to compute with the definitions and give automatic proofs of the properties of the model. We use this implementation to evaluate the model on a series of datasets. Through this analysis, we characterize the types of datasets that are more, or less, suitable to be described by the theory.

AILAW Journal 2026 Journal Article

Hierarchical models of precedential constraint

• Wijnand van Woerkom
• Davide Grossi
• Henry Prakken
• Bart Verheij

Abstract In recent years, models of a fortiori argumentation from the field of artificial intelligence and law, developed to describe legal case-based reasoning based on precedent, have been successfully applied to improve interpretability of data-driven decision systems. To aid with these applications, we further develop the theory of a fortiori case-based reasoning by extending the knowledge representations on which these models operate. More specifically, we modify the representations to accommodate incomplete information, as well as to incorporate both dimensional (as opposed to binary) and hierarchical (as opposed to unstructured) information. This results in four models—one for each combination of accommodating dimensional or hierarchical information. We investigate their formal properties, and find they are monotonic with respect to the addition of new precedents and of new facts, and that some are conservative extensions of other models. In addition, we exemplify each through a running example from the penitentiary law domain.

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.

JAIR Journal 2024 Journal Article

A Fortiori Case-Based Reasoning: From Theory to Data

• Wijnand van Woerkom
• Davide Grossi
• Henry Prakken
• Bart Verheij

The widespread application of uninterpretable machine learning systems for sensitive purposes has spurred research into elucidating the decision-making process of these systems. These efforts have their background in many different disciplines, one of which is the field of AI & law. In particular, recent works have observed that machine learning training data can be interpreted as legal cases. Under this interpretation, the formalism developed to study case law, called the theory of precedential constraint, can be used to analyze the way in which machine learning systems draw on training data—or should draw on them—to make decisions. In the present work, we advance the theory underlying these explanation methods, by relating it to order theory and logic. This allows us to write a software implementation of the theory that can be used to compute with the definitions and give automatic proofs of the properties of the model. We use this implementation to evaluate the model on a series of datasets. Through this analysis, we characterize the types of datasets that are more, or less, suitable to be described by the theory.

AIJ Journal 2024 Journal Article

An abstract and structured account of dialectical argument strength

• Henry Prakken

This paper presents a formal model of dialectical argument strength in terms of the number of ways in which an argument can be successfully attacked in expansions of an abstract argumentation framework. First a model is proposed that is abstract but designed to avoid overly limiting assumptions on instantiations or dialogue contexts. It is then shown that most principles for argument strength proposed in the literature fail to hold for the proposed notions of dialectical strength, which clarifies the rational foundations of these principles and highlights the importance of distinguishing between kinds of argument strength, in particular logical, dialectical and rhetorical argument strength. The abstract model is then instantiated with ASPIC + to test the claim that it does not make overly limiting assumptions on the structure of arguments and the nature of their relations.

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

Relating Abstract and Structured Accounts of Argumentation Dynamics: the Case of Expansions

• Henry Prakken

This paper proposes a structured variant in ASPIC+ of the notion of expansions of abstract argumentation frameworks. The purpose of this is threefold: studying what it takes to instantiate the abstract notion of expansions with a structured account of argumentation, studying to which extent assumptions implicitly made at the abstract level hold for structured instantiations and studying which potentially interesting distinctions can be made at the structured level that cannot be expressed at the abstract level.

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

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.

AILAW Journal 2021 Journal Article

A formal analysis of some factor- and precedent-based accounts of precedential constraint

• Henry Prakken

Abstract In this paper several recent factor- and dimension-based models of precedential constraint are formally investigated and an alternative dimension-based model is proposed. Simple factor- and dimension-based syntactic criteria are identified for checking whether a decision in a new case is forced, in terms of the relevant differences between a precedent and a new case, and the difference between absence of factors and negated factors in factor-based models is investigated. Then Horty’s and Rigoni’s recent dimension-based models of precedential constraint are critically examined. An alternative to their reason models is proposed which is less expressive but arguably easier to apply in practice.

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 2018 Journal Article

A new use case for argumentation support tools: supporting discussions of Bayesian analyses of complex criminal cases

• Henry Prakken

Abstract In this paper a new use case for legal argumentation support tools is considered: supporting discussions about analyses of complex criminal cases with the help of Bayesian probability theory. By way of a case study, two actual discussions between experts in court cases are analysed on their argumentation structure. In this study the usefulness of several recognised argument schemes is confirmed, a new argument scheme for arguments from statistics are proposed, and an analysis is given of debates between experts about the validity of their arguments. From a practical point of view the case study yields insights into the design of support software for discussions about Bayesian analyses of complex criminal cases.

AIJ Journal 2018 Journal Article

Corrigendum to “A general account of argumentation with preferences” [Artif. Intell. 195 (2013) 361–397]

• Sanjay Modgil
• Henry Prakken

ASPIC + is a general framework for structured argumentation that allows for a considerable degree of freedom as to the knowledge representation choices made in specifying the premises and rules from which arguments are constructed, and the preferences used to determine which attacks amongst constructed arguments succeed as defeats. On the other hand, the framework provides guidelines for making these choices, such that adherence to these guidelines suffices to guarantee satisfaction of the consistency and closure postulates. In particular, guidelines are given for selecting ways in which to compare the sets of defeasible constituents of arguments in order that the defined preference relations over arguments guarantee satisfaction of the rationality postulates. However, it has recently been noted that the way in which these set comparisons are made, and the guidelines for choosing these comparisons, admit counter-examples to these postulates. This research note proposes simple revisions to the ASPIC + framework as defined in [3]. In this way, the counter-examples are avoided and rationality is preserved.

KR Conference 2018 Conference Paper

Probabilistic Strength of Arguments with Structure

• Henry Prakken

This paper investigates the relation between abstract and structured accounts of probabilistic argumentation. The AS- PIC+ framework is applied to default reasoning with probabilistic generalisations, using the idea that the probability of an argument is the probability of the conjunction of all its premises and conclusions. Based on this idea, two notions of internal and dialectical argument strength are defined and compared. The resulting account is then related to Hunter & Thimm’s epistemic approach to abstract probabilistic argumentation.

FLAP Journal 2017 Journal Article

Abstract Rule-Based Argumentation.

• Sanjay Modgil
• Henry Prakken

This article reviews abstract rule-based approaches to argumentation, in particular the ASPIC + framework. In ASPIC + and its predecessors, going back to the seminal work of John Pollock, arguments can be formed by combining strict and defeasible inference rules and conflicts between arguments can be resolved in terms of a preference relation on arguments. This results in abstract argumentation frameworks (a set of arguments with a binary relation of defeat), so that arguments can be evaluated with the theory of abstract argumentation. First the basic ASPIC + framework is reviewed, possible ways to instantiate it are discussed and how these instantiations can satisfy closure and consistency properties. Then the relation between ASPIC + and other work in formal argumentation and nonmonotonic logic is discussed, including a review of how other approaches can be reconstructed as instantiations of ASPIC +. Further developments and variants of the basic ASPIC + framework are also reviewed, including developments with alternative or generalised notions of attack and defeat and variants with further constraints on arguments. Finally, implementations and applications of ASPIC + are briefly reviewed and some open problems and avenues for further research are discussed.

FLAP Journal 2017 Journal Article

Historical Overview of Formal Argumentation.

• Henry Prakken

This article gives an overview of the history of formal argumentation in terms of a distinction between argumentation-based inference and argumentationbased dialogue. Systems for argumentation-based inference are about which conclusions can be drawn from a given body of possibly incomplete, inconsistent of uncertain information. They ultimately define a nonmonotonic notion of logical consequence, in terms of the intermediate notions of argument construction, argument attack and argument evaluation, where arguments are seen as constellations of premises, conclusions and inferences. Systems for argumentationbased dialogue model argumentation as a kind of verbal interaction aimed at resolving conflicts of opinion. They define argumentation protocols, that is, the rules of the argumentation game, and address matters of strategy, that is, how to play the game well. For both aspects of argumentation the main formal and computational models are reviewed and their main historical influences are sketched. Then some main applications areas are briefly discussed.

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 2017 Journal Article

On the problem of making autonomous vehicles conform to traffic law

• Henry Prakken

Abstract Autonomous vehicles are one of the most spectacular recent developments of Artificial Intelligence. Among the problems that still need to be solved before they can fully autonomously participate in traffic is the one of making their behaviour conform to the traffic laws. This paper discusses this problem by way of a case study of Dutch traffic law. First it is discussed to what extent Dutch traffic law exhibits features that are traditionally said to pose challenges for AI & Law models, such as exceptions, rule conflicts, open texture and vagueness, rule change, and the need for commonsense knowledge. Then three approaches to the design of law-conforming AV are evaluated in light of the challenges posed by Dutch traffic law, which includes an assessment of the usefulness of AI & Law models of nonmonotonic reasoning, argumentation and case-based reasoning.

AILAW Journal 2016 Journal Article

A method for explaining Bayesian networks for legal evidence with scenarios

• Charlotte S. Vlek
• Henry Prakken
• Silja Renooij
• Bart Verheij

Abstract In a criminal trial, a judge or jury needs to reason about what happened based on the available evidence, often including statistical evidence. While a probabilistic approach is suitable for analysing the statistical evidence, a judge or jury may be more inclined to use a narrative or argumentative approach when considering the case as a whole. In this paper we propose a combination of two approaches, combining Bayesian networks with scenarios. Whereas a Bayesian network is a popular tool for analysing parts of a case, constructing and understanding a network for an entire case is not straightforward. We propose an explanation method for understanding a Bayesian network in terms of scenarios. This method builds on a previously proposed construction method, which we slightly adapt with the use of scenario schemes for the purpose of explaining. The resulting structure is explained in terms of scenarios, scenario quality and evidential support. A probabilistic interpretation of scenario quality is provided using the concept of scenario schemes. Finally, the method is evaluated by means of a case study.

JAIR Journal 2016 Journal Article

Two Aspects of Relevance in Structured Argumentation: Minimality and Paraconsistency

• Diana Grooters
• Henry Prakken

This paper studies two issues concerning relevance in structured argumentation in the context of the ASPIC+ framework, arising from the combined use of strict and defeasible inference rules. One issue arises if the strict inference rules correspond to classical logic. A longstanding problem is how the trivialising effect of the classical Ex Falso principle can be avoided while satisfying consistency and closure postulates. In this paper, this problem is solved by disallowing chaining of strict rules, resulting in a variant of the ASPIC+ framework called ASPIC*, and then disallowing the application of strict rules to inconsistent sets of formulas. Thus in effect Rescher & Manor's paraconsistent notion of weak consequence is embedded in ASPIC*. Another issue is minimality of arguments. If arguments can apply defeasible inference rules, then they cannot be required to have subset-minimal premises, since defeasible rules based on more information may well make an argument stronger. In this paper instead minimality is required of applications of strict rules throughout an argument. It is shown that under some plausible assumptions this does not affect the set of conclusions. In addition, circular arguments are in the new ASPIC* framework excluded in a way that satisfies closure and consistency postulates and that generates finitary argumentation frameworks if the knowledge base and set of defeasible rules are finite. For the latter result the exclusion of chaining of strict rules is essential. Finally, the combined results of this paper are shown to be a proper extension of classical-logic argumentation with preferences and defeasible rules.

AIJ Journal 2015 Journal Article

Law and logic: A review from an argumentation perspective

• Henry Prakken
• Giovanni Sartor

This article reviews legal applications of logic, with a particularly marked concern for logical models of legal argument. We argue that the law is a rich test bed and important application field for logic-based AI research. First applications of logic to the representation of legal regulations are reviewed, where the main emphasis is on representation and where the legal conclusions follow from that representation as a matter of deduction. This includes the representation of deontic concepts, normative positions, legal ontologies, time and change. Then legal applications of logic are reviewed where legal rules are not just applied but are the object of reasoning and discourse. This includes arguing about applying statutory rules in unforeseen circumstances, interpretative reasoning in light of the facts of a case, and evidential reasoning to establish the facts of a case. This part of the review has special emphasis on argumentation-based approaches. This also holds for the final part, which discusses formal models of legal procedure and of multi-agent interaction in legal proceedings. The review concludes with identifying some of the main open research problems. The review shows that modern legal applications of logic confirm the recent trend of widening the scope of logic from deduction to information flow, argumentation and interaction.

AILAW Journal 2014 Journal Article

Building Bayesian networks for legal evidence with narratives: a case study evaluation

• Charlotte S. Vlek
• Henry Prakken
• Silja Renooij
• Bart Verheij

Abstract In a criminal trial, evidence is used to draw conclusions about what happened concerning a supposed crime. Traditionally, the three main approaches to modeling reasoning with evidence are argumentative, narrative and probabilistic approaches. Integrating these three approaches could arguably enhance the communication between an expert and a judge or jury. In previous work, techniques were proposed to represent narratives in a Bayesian network and to use narratives as a basis for systematizing the construction of a Bayesian network for a legal case. In this paper, these techniques are combined to form a design method for constructing a Bayesian network based on narratives. This design method is evaluated by means of an extensive case study concerning the notorious Dutch case of the Anjum murders.

ECAI Conference 2014 Conference Paper

On support relations in abstract argumentation as abstractions of inferential relations

• Henry Prakken

Arguably the significance of an abstract model of argumentation depends on the range of realistic instantiations it allows. This paper therefore investigates for three frameworks for abstract argumentation with support relations whether they can be instantiated with the ASPIC+framework for structured argumentation. Both evidential argumentation systems and a simple extension of Dung's abstract frameworks with support relations proposed by Dung & Thang (2014) are shown to allow such an instantiation. However, for bipolar argumentation frameworks a positive result is only obtained for variants with only direct and secondary attacks; counterexamples are provided for variants with supported attacks, even for the special case of deductive support.

AIJ Journal 2013 Journal Article

A general account of argumentation with preferences

• Sanjay Modgil
• Henry Prakken

This paper builds on the recent ASPIC + formalism, to develop a general framework for argumentation with preferences. We motivate a revised definition of conflict free sets of arguments, adapt ASPIC + to accommodate a broader range of instantiating logics, and show that under some assumptions, the resulting framework satisfies key properties and rationality postulates. We then show that the generalised framework accommodates Tarskian logic instantiations extended with preferences, and then study instantiations of the framework by classical logic approaches to argumentation. We conclude by arguing that ASPIC + ʼs modelling of defeasible inference rules further testifies to the generality of the framework, and then examine and counter recent critiques of Dungʼs framework and its extensions to accommodate preferences.

AILAW Journal 2012 Journal Article

Reconstructing Popov v. Hayashi in a framework for argumentation with structured arguments and Dungean semantics

• Henry Prakken

Abstract In this article the argumentation structure of the court’s decision in the Popov v. Hayashi case is formalised in Prakken’s (Argument Comput 1: 93–124; 2010 ) abstract framework for argument-based inference with structured arguments. In this framework, arguments are inference trees formed by applying two kinds of inference rules, strict and defeasible rules. Arguments can be attacked in three ways: attacking a premise, attacking a conclusion and attacking an inference. To resolve such conflicts, preferences may be used, which leads to three corresponding kinds of defeat, after which Dung’s (Artif Intell 77: 321–357; 1995 ) abstract acceptability semantics can be used to evaluate the arguments. In the present paper the abstract framework is instantiated with strict inference rules corresponding to first-order logic and with defeasible inference rules for defeasible modus ponens and various argument schemes. The main techniques used in the formal reconstruction of the case are rule-exception structures and arguments about rule validity. Arguments about socio-legal values and the use of precedent cases are reduced to arguments about rule validity. The tree structure of arguments, with explicit subargument relations between arguments, is used to capture the dependency relations between the elements of the court’s decision.

AAMAS Conference 2012 Conference Paper

Testing the Benefits of Structured Argumentation in Multi-Agent Deliberation Dialogues

• Eric Kok
• John-Jules Meyer
• Henry Prakken
• GERARD VREESWIJK

Work on argumentation-based dialogue systems often assumes that the adoption of argumentation leads to improved efficiency and effectiveness. Several studies have taken an experimental approach to prove these alleged benefits, but none has so far supported the expressiveness of a logic for structured argumentation. This paper shows how the use of argumentation in deliberation dialogues can be tested while supporting goal-based agents that use the ASPIC framework for structured argumentation.

EUMAS Conference 2011 Conference Paper

A Methodology for the Generation of Multi-agent Argumentation Dialogue Scenarios

• Eric M. Kok
• John-Jules Ch. Meyer
• Herre van Oostendorp
• Henry Prakken
• Gerard Vreeswijk

Abstract Increasingly research into the uses of argumentation in multi-agent dialogues takes an experimental approach. Such studies explore how agents can successfully employ argumentation besides the best and worst case situations of formal analysis. While a vital part in these experiments is influenced by the scenarios from which dialogues are generated, there is very little research on how these can be generated in a meaningful way, respecting the characteristics of the underlying dialogue problem. This paper proposes, by means of an example system for deliberation dialogues, a methodology for the construction and evaluation of a scenario generation process. It is shown how scenarios can accommodate argumentation with structured arguments and how it is tested whether the generated scenarios are interesting for experimentation.

IJCAI Conference 2011 Conference Paper

Relating Carneades with Abstract Argumentation

• Bas van Gijzel
• Henry Prakken

Carneades is a recently proposed formalism for structured argumentation with varying proof standards. An open question is its relation with Dung's seminal abstract approach to argumentation. In this paper the two formalisms are formally related by translating Carneades into ASPIC+, another recently proposed formalism for structured argumentation. Since ASPIC+ is defined to generate Dung-style abstract argumentation frameworks, this in effect translates Carneades graphs into abstract argumentation frameworks. It is proven that Carneades always induces a unique Dung extension, which is the same in all of Dung's semantics.

IJCAI Conference 2011 Conference Paper

Revisiting Preferences and Argumentation

• Sanjay Modgil
• Henry Prakken

The ASPIC+ framework is intermediate in abstraction between Dung's argumentation framework and concrete instantiating logics. This paper generalises ASPIC+ to accommodate classical logic instantiations, and adopts a new proposal for evaluating extensions: attacks are used to define the notion of conflict-free sets, while the defeats obtained by applying preferences to attacks, are exclusively used to determine the acceptability of arguments. Key properties and rationality postulates are then shown to hold for the new framework.

AILAW Journal 2010 Journal Article

A hybrid formal theory of arguments, stories and criminal evidence

• Floris J. Bex
• Peter J. van Koppen
• Henry Prakken
• Bart Verheij

Abstract This paper presents a theory of reasoning with evidence in order to determine the facts in a criminal case. The focus is on the process of proof, in which the facts of the case are determined, rather than on related legal issues, such as the admissibility of evidence. In the literature, two approaches to reasoning with evidence can be distinguished, one argument-based and one story-based. In an argument-based approach to reasoning with evidence, the reasons for and against the occurrence of an event, e. g. , based on witness testimony, are central. In a story-based approach, evidence is evaluated and interpreted from the perspective of the factual stories as they may have occurred in a case, e. g. , as they are defended by the prosecution. In this paper, we argue that both arguments and narratives are relevant and useful in the reasoning with and interpretation of evidence. Therefore, a hybrid approach is proposed and formally developed, doing justice to both the argument-based and the narrative-based perspective. By the formalization of the theory and the associated graphical representations, our proposal is the basis for the design of software developed as a tool to make sense of the evidence in complex cases.

AILAW Journal 2010 Journal Article

Using argument schemes for hypothetical reasoning in law

• Trevor Bench-Capon
• Henry Prakken

Abstract This paper studies the use of hypothetical and value-based reasoning in US Supreme-Court cases concerning the United States Fourth Amendment. Drawing upon formal AI & Law models of legal argument a semi-formal reconstruction is given of parts of the Carney case, which has been studied previously in AI & law research on case-based reasoning. As part of the reconstruction, a semi-formal proposal is made for extending the formal AI & Law models with forms of metalevel reasoning in several argument schemes. The result is compared with Rissland’s ( 1989 ) analysis in terms of dimensions and Ashley’s ( 2008 ) analysis in terms of his process model of legal argument with hypotheticals.

AILAW Journal 2008 Journal Article

A formal model of adjudication dialogues

• Henry Prakken

Abstract This article presents a formal dialogue game for adjudication dialogues. Existing AI & law models of legal dialogues and argumentation-theoretic models of persuasion are extended with a neutral third party, to give a more realistic account of the adjudicator’s role in legal procedures. The main feature of the model is a division into an argumentation phase, where the adversaries plea their case and the adjudicator has a largely mediating role, and a decision phase, where the adjudicator decides the dispute on the basis of the claims, arguments and evidence put forward in the argumentation phase. The model allows for explicit decisions on admissibility of evidence and burden of proof by the adjudicator in the argumentation phase. Adjudication is modelled as putting forward arguments, in particular undercutting and priority arguments, in the decision phase. The model reconciles logical aspects of burden of proof induced by the defeasible nature of arguments with dialogical aspects of burden of proof as something that can be allocated by explicit decisions on legal grounds.

JELIA Conference 2008 Conference Paper

Combining Modes of Reasoning: An Application of Abstract Argumentation

• Henry Prakken

Abstract Many reasoning problems involve subproblems that can be solved in different ways. Therefore, hybrid reasoning architectures have long been a research topic in AI. However, most work in this area has either focused on particular combinations of reasoning methods or has ignored the problem of handling alternative solutions to subproblems. The present paper proposes an abstract framework for combining modes of reasoning and handling alternative solutions. It is argued that current abstract argumentation systems are either too abstract or too specific for this purpose, so that an intermediate level of abstraction is needed.

AILAW Journal 2008 Journal Article

Formalising ordinary legal disputes: a case study

• Henry Prakken

Abstract This paper presents a formal reconstruction of a Dutch civil legal case in Prakken’s formal model of adjudication dialogues. The object of formalisation is the argumentative speech acts exchanged during the dispute by the adversaries and the judge. The goal of this formalisation is twofold: to test whether AI & law models of legal dialogues in general, and Prakken’s model in particular, are suitable for modelling particular legal procedures; and to learn about the process of formalising an actual legal dispute.

AIJ Journal 2007 Journal Article

The Carneades model of argument and burden of proof

• Thomas F. Gordon
• Henry Prakken
• Douglas Walton

We present a formal, mathematical model of argument structure and evaluation, taking seriously the procedural and dialogical aspects of argumentation. The model applies proof standards to determine the acceptability of statements on an issue-by-issue basis. The model uses different types of premises (ordinary premises, assumptions and exceptions) and information about the dialectical status of statements (stated, questioned, accepted or rejected) to allow the burden of proof to be allocated to the proponent or the respondent, as appropriate, for each premise separately. Our approach allows the burden of proof for a premise to be assigned to a different party than the one who has the burden of proving the conclusion of the argument, and also to change the burden of proof or applicable proof standard as the dialogue progresses from stage to stage. Useful for modeling legal dialogues, the burden of production and burden of persuasion can be handled separately, with a different responsible party and applicable proof standard for each. Carneades enables critical questions of argumentation schemes to be modeled as additional premises, using premise types to capture the varying effect on the burden of proof of different kinds of questions.

KER Journal 2006 Journal Article

Formal systems for persuasion dialogue

• Henry Prakken

This article reviews formal systems that regulate persuasion dialogues. In such dialogues two or more participants aim to resolve a difference of opinion, each trying to persuade the other participants to adopt their point of view. Systems for persuasion dialogue have found application in various fields of computer science, such as non-monotonic logic, artificial intelligence and law, multi-agent systems, intelligent tutoring and computer-supported collaborative argumentation. Taking a game-theoretic view on dialogue systems, this review proposes a formal specification of the main elements of dialogue systems for persuasion and then uses it to critically review some of the main formal systems for persuasion. The focus of this review will be on regulating the interaction between agents rather than on the design and behaviour of individual agents within a dialogue.

AAMAS Conference 2005 Conference Paper

A Verifiable Protocol for Arguing about Rejections in Negotiation

• Jelle van Veenen
• Henry Prakken

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.

AILAW Journal 2002 Journal Article

An exercise in formalising teleological case-based reasoning

• Henry Prakken

This paper takes up Berman and Hafner's (1993) challenge to model legal case-based reasoning not just in terms of factual similarities and differences but also in terms of the values that are at stake. The formal framework of Prakken and Sartor (1998) is applied to examples of case-based reasoning involving values, and a method for formalising such examples is proposed. The method makes it possible to express that a case should be decided in a certain way because that advances certain values. The method also supports the comparison of conflicting precedents in terms of values, and it supports debates on the relevance of distinctions in terms of values.

NMR Workshop 2002 Conference Paper

Intuitions and the modelling of defeasible reasoning: some case studies

• Henry Prakken

The purpose of this paper is to address some criticisms recently raised by John Horty in two articles against the validity of two commonly accepted defeasible reasoning patterns, viz. reinstatement and floating conclusions. I shall argue that Horty’s counterexamples, although they significantly raise our understanding of these reasoning patterns, do not show their invalidity. Some of them reflect patterns which, if made explicit in the formalisation, avoid the unwanted inference without having to give up the criticised inference principles. Other examples seem to involve hidden assumptions about the specific problem which, if made explicit, are nothing but extra information that defeat the defeasible inference. These considerations will be put in a wider perspective by reflecting on the nature of defeasible reasoning principles as principles of justified acceptance rather than ‘real’ logical inference.

JELIA Conference 2000 Conference Paper

Credulous and Sceptical Argument Games for Preferred Semantics

• Gerard Vreeswijk
• Henry Prakken

Abstract This paper presents dialectical proof theories for Dung’s pre-ferred semantics of defeasible argumentation. The proof theories have the form of argument games for testing membership of some (credulous reasoning) or all preferred extensions (sceptical reasoning). The credulous proof theory is for the general case, while the sceptical version is for the case where preferred semantics coincides with stable semantics. The development of these argument games is especially motivated by applica-tions of argumentation in automated negotiation, mediation of collective discussion and decision making, and intelligent tutoring.

AILAW Journal 2000 Journal Article

Introduction: Dialectical legal argument: Formal and informal models

• Eveline Feteris
• Henry Prakken

JELIA Conference 2000 Conference Paper

On Dialogue Systems with Speech Acts, Arguments, and Counterarguments

• Henry Prakken

Abstract This paper proposes a formal framework for argumentative dialogue systems with the possibility of counterargument. The framework allows for claiming, challenging, retracting and conceding propositions. It also allows for exchanging arguments and counterarguments for propo-sitions, by incorporating argument games for nonmonotonic logics. A key element of the framework is a precise definition of the notion of relevance of a move, which enables flexible yet well-behaved protocols.

AILAW Journal 1996 Journal Article

Editors' introduction

• Henry Prakken
• Giovanni Sartor