My research focuses on artificial intelligence and argumentation, often with the law as application domain. See the handbook chapter `Chapter 11: Artificial intelligence and argumentation'. In the chapter, also the connection to artificial intelligence and law research is discussed. Currently, I work on the connections between knowledge, data and inference in artificial intelligence.

In a series of papers, I am studying the logic of argumentation, in which case models provide a formal semantics for arguments. The case model formalism was first published in the 2016 JELIA conference paper `Correct Grounded Reasoning with Presumptive Arguments' (building on papers presented at JELIA 2012 and COMMA 2014), and formalizes the semi-formally presented ideas in the 2014 journal paper `To Catch a Thief With and Without Numbers' on evidential reasoning. The formalism was inspired by the setting of reasoning with evidence, where qualitative and quantitative reasoning methods are used side-by-side. The case model formalism was applied to the combination of arguments, scenarios and probabilities as normative tools in evidential reasoning (in the 2017 journal paper `Proof With and Without Probabilities'), to value-guided argumentation in the context of ethical systems design (in the 2016 journal paper `Formalizing Value-Guided Argumentation for Ethical Systems Design'), and to the modeling of reasoning with arguments, rules and cases in the law (in the 2017 ICAIL conference paper `Formalizing Arguments, Rules and Cases').

I recently led a research project on the connections between arguments, scenarios and probabilities in forensic reasoning with evidence, funded by the NWO Forensic Science program (2012-2017). In the project, methods for the design and understanding of Bayesian Networks were developed using scenarios (Charlotte Vlek) and arguments (Sjoerd Timmer). Project web site: The 2016 journal paper `Arguments, Scenarios and Probabilities: Connections Between Three Normative Frameworks for Evidential Reasoning' provides an overview of approaches in the project. Key research output of the project is as follows:
    • A method to manually design a Bayesian Network incorporating hypothetical scenarios and the available evidence, with a case study testing the design method (Vlek et al., 2014);
    • A method to generate a structured explanatory text of a Bayesian Network modeled according to this method, with a case study testing the explanation method (Vlek et al., 2016);
    • A method to incorporate argument schemes and their critical questions in a Bayesian Network (Timmer et al., 2015);
    • An algorithm to extract argumentative information from a Bayesian Network modeling hypotheses and evidence (Timmer et al., 2017).

      In the NWO VICI project led by Rineke Verbrugge, I cosupervised Harmen de Weerd during his research on studying higher-order theory of mind using agent-based simulations. He showed how higher-order theory of mind plays a role in competitive, cooperative and mixed-motive settings, such as negotiation.

      A semi-formal impression of my perspective on AI & law is available in this 2005 interview (in Dutch; pdf) or this 2007 coffeehouse conversation. My views on semi-formal argumentation are explained in this 2009 text where I trace Toulmin's footprints in AI. My 2005 book Virtual arguments contains a lot of information about my work on the design and logical underpinning of argumentation software. ArguMed based on DefLog is the software version to focus on; it is Dung compliant (stable semantics), has pros and cons (also for and against support/attack links), and has been assessed by a protocolled qualitative user evaluation. The book has more than the 2003 Artificial intelligence journal paper. A 2007 paper gives an update, and a perspective on increasing the usefulness of argumentation software for professionals. That paper also contains an accessible version of my view on entangled dialectical arguments (and associated diagrams), of which the logical formalization is studied in the 2003 paper on DefLog. A deviant strand of argumentation software, focusing more on content and less on argument diagramming, is the ArguGuide tool developed with Maaike Schweers, Stijn Colen and Fokie Cnossen (see ICAIL 2009 for a very short description of the statistically significant evidence that we have showing that the ArguGuide design improves performance on a case solving task).

      I have always paid a lot of attention to the naturalness of the argument/reasoning models I developed (although this may not always be obvious). Reason-Based Logic (with Jaap Hage) is a good example of this (see e.g. my 1996 dissertation). Also noteworthy in this respect are this 1997 attempt (with Jaap Hage and Arno Lodder) to faithfully model a part of Dutch tort law, and a second improved attempt (with Jaap Hage and Gerrit van Maanen; only available in Dutch). A very sobering, hence fruitful, experience in this respect has been the development of teaching material for students of Dutch law to improve their argumentative skills. It is in its third printing (2008). Even my DefLog formalism aims to provide a natural conceptualisation of argumentation. (That is why I e.g. prefer to speak of arguments justifying prima facie conclusions and not of justified arguments.) My 2005 interpretation and extension of Toulmin's argument model/diagram in terms of DefLog is an indication of its naturalness (for more on Toulmin see this 2006 volume coedited with David Hitchcock and this 2009 paper on the reception of Toulmin's ideas in AI). Another such indication is my 2003 treatment of Walton's argumentation schemes, where I treat argumentation schemes as a kind of semi-formal rules of inference with exceptions that can be found and systematized using a knowledge engineering approach. An early incarnation of that work was presented at ICAIL 2001, formally worked out in the full report. The idea of argumentation schemes as contextual, defeasible, semi-formal rules of inference was already used in my work on Reason-Based Logic (with Jaap Hage; e.g., chapter 2, section 6 of my 1996 dissertation). The associated 'philosophy of logic' is explained in my 1999 paper 'Logic, context and valid inference. Or: Can there be a logic of law?', a personal favorite. For me, argumentation schemes are a continuation of Toulmin's ideas on warrants: contextual, defeasible, semi-formal. This perspective is explained and embedded in a research tradition in my 2009 book chapter on how semi-formal, defeasible argumentation schemes creep into logic.

      My interest in reasoning with evidence and legal proof started in Maastricht (see the 2000 text on the connections between argumentation and stories that I wrote for Hans Crombag). In Groningen this work really got off the ground by Floris Bex's PhD research (2005-2009), in a joint project with Henry Prakken and Peter van Koppen (and also Susan van den Braak, Gerard Vreeswijk and Herre van Oostendorp; see an early overview paper, this 2007 paper and the project's page). The 2009 volume edited with Hendrik Kaptein and Henry Prakken is also on this theme. It includes a chapter on reconstructing the anchored narratives theory using argumentation schemes.

      In 1996 I proposed two additional semantics for abstract argumentation in the sense of Dung 1995: stage extensions and admissible stage extensions. The latter now go by the name of semi-stable extensions (see Caminada's 2006 work). I continued this line of work in a more expressive language (see the 2003 paper on DefLog), in order to incorporate pros and cons, and in an attempt to close the gap between argumentation formalisms and logic. The DefLog language not only allows the expression of support and attack, but also of reasoning about support and attack. The latter was called entanglement by Bram Roth. ArguMed based on DefLog is an implementation of DefLog (computing its Dung-faithful version of stable semantics) and the associated argument diagrams. For abstract argumentation I have also implemented a software tool that computes small admissible sets and the grounded, preferred, stable and semi-stable semantics for abstract argumentation (see this 2007 publication).

      In 1996 I received my doctoral degree by defending my dissertation, entitled 'Rules, Reasons, Arguments. Formal studies of argumentation and defeat'. I have contributed to Jaap Hage's Reason-Based Logic, a model of rules and reasons, have developed CumulA, a model of argumentation with arguments and counterarguments in stages, have provided an abstract model of the law in terms of states of affairs, events, and rules (with Jaap Hage), and have implemented Argue! and ArguMed, two systems for automated argument assistance. I have also developed the logical system DefLog, focusing on the interpretation of prima facie justified assumptions. In collaboration with Bram Roth I have studied case-based reasoning in terms of the comparison of the dialectical arguments in cases. This resulted in Roth's dissertation Case-based reasoning in the law. A formal theory of reasoning by case comparison (2003), written under my supervision. My research about argument assistance systems resulted in a publication in the Artificial Intelligence journal and a book, entitled Virtual Arguments On the Design of Argument Assistants for Lawyers and Other Arguers .

      Key words: legal reasoning, defeasible reasoning, dialectical argumentation, computational dialectics, nonmonotonic logics, argument defeat, artificial intelligence and law, legal ontology, rules and principles, argument mediation, argument assistance.


BNAIC 2017 (November 8-9, 2017)

The 29th Benelux Conference on Artificial Intelligence (Groningen)

Kennisdiner `The Fiction of Reality' (September 18, 2017)

Diner met sprekers, Studium Generale Groningen (met historicus Jan Blaauw, medisch onderzoeker Désirée Goubert, theatermaakster Sarah Moeremans). Locatie: Grand Theatre. Catering: Kruimels. Verslag in Universiteitskrant

Inaugural lecture (September 12, 2017)

Argumenten voor goede kunstmatige intelligentie (Arguments for good artificial intelligence)

Vacancies: fully funded PhD positions in artificial intelligence and argumentation (Apply before July 15, 2017)

Projects The value of data and Home robotics
- In your motivation letter, you should apply for a specific project or projects.
- There are restrictions: you should not have resided or carried out your main activity in The Netherlands for more than 12 months in the three years before July 15, 2017.

ICAIL 2017 conference paper (2017)

Formalizing Arguments, Rules and Cases

Workshop King's College, London (2017)

Evidence & Decision Making in the Law: Theoretical, Computational and Empirical Approaches (organized with Marcello Di Bello)

Artificial Intelligence and Law journal special issue (2017)

Special issue Artificial Intelligence for Justice (AI4J) (with Floris Bex, Henry Prakken and Tom van Engers)

Artificial Intelligence and Law journal paper (2017)

Proof With and Without Probabilities. Correct Evidential Reasoning with Presumptive Arguments, Coherent Hypotheses and Degrees of Uncertainty

Journal of Autonomous Agents and Multi-Agent Systems paper (2017)

Negotiating with Other Minds. The Role of Recursive Theory of Mind in Negotiation with Incomplete Information (with Harmen de Weerd and Rineke Verbrugge)

Dissertation defence (2017)

On Wednesday February 1, 2017, Sjoerd Timmer
defends his dissertation `Designing and Understanding Forensic Bayesian Networks using Argumentation' in Utrecht.

International Journal of Approximate Reasoning journal paper (2017)

A two-phase method for extracting explanatory arguments from Bayesian networks (with Sjoerd Timmer, John-Jules Meyer, Henry Prakken and Silja Renooij)

JURIX conference paper on ethical systems design (2016)

Arguments for Ethical Systems Design

Artificial Intelligence and Law journal paper on ethical systems design (2016)

Formalizing Value-Guided Argumentation for Ethical Systems Design

JELIA conference paper (2016)

Correct Grounded Reasoning with Presumptive Arguments

Final symposium NWO Forensic Science research program (2016)

Presentation of the research project on statistics, argumentation and scenarios in forensic reasoning (report by ZonMW in Dutch)

Invited researcher at the Isaac Newton Institute for Mathematical Sciences, University of Cambridge (2016)

Scientific programme Probability and Statistics in Forensic Science

Workshop and dissertation defence (2016)

Friday October 28, 2016: Dissertation defence Charlotte Vlek (press report, download dissertation)
Thursday October 27, 2016: Workshop Beyond a Reasonable Doubt: Scenarios and Bayesian Networks for Analyzing Forensic Evidence

Invited graduate course Second Summer School of Argumentation (2016)

University of Potsdam, Campus Griebnitzsee

Artificial Intelligence for Justice, workshop at ECAI (2016)

The Hague, August 30, 2016

Argument and Computation journal (2016)

First open access issue online

Artificial Intelligence and Law journal paper (2016)

A Method for Explaining Bayesian Networks for Legal Evidence with Scenarios (with Charlotte Vlek, Henry Prakken and Silja Renooij)

Stanford CodeX FutureLaw conference (2016)

Computational Law Update, speaker (invited)

Faculty Spotlight talk (2016)

Arguments for Understanding our Complex World

Law, Probability and Risk journal paper (2016)

Arguments, Scenarios and Probabilities: Connections Between Three Normative Frameworks for Evidential Reasoning (with Floris Bex, Sjoerd Timmer, Charlotte Vlek, John-Jules Meyer, Silja Renooij and Henry Prakken)

Book Virtual Arguments, Chinese translation (2016)

China University of Political Science and Law Press, series editor Professor Minghui Xiong (Sun Yat-Sen University, Institute of Logic and Cognition), translation Wu Zhou

PhD defense Harmen de Weerd and associated mini-symposium (2015)

Harmen de Weerd's dissertation: 'If You Know What I Mean. Agent-Based Models for Understanding The Function of Higher-Order Theory of Mind' (promotor: Rineke Verbrugge, copromotor: Bart Verheij)

Workshop Bielefeld, Germany (2015)

Models of Rational Proof in Criminal Law (organized by Floris Bex, Anne Ruth Mackor and Henry Prakken; with support from our NWO Forensic Science project)

Workshop University of San Diego, California (2015)

Studying Evidence in the Law - ICAIL 2015 Workshop: Formal, Computational and Philosophical Methods

Stanford CodeX FutureLaw conference 2015 (2015)

Panel New Breakthroughs in Computational Law, invited moderator

Workshop University of Groningen (2015)

Forensic Relevance of Bayesian Networks (language: Dutch)

Keynote lecture SMART Cognitive Science International Colloquium, Communication and Agency workshop (2015)

Arguments, scenarios and probabilities: how to catch a thief with and without numbers

Presentation at the Effacts LegalTech event, Amsterdam (2015)

Argumentation Technology, Or: How the Law Is Changing Artificial Intelligence

Handbook of Argumentation Theory (2014)

with a chapter on Argumentation and Artificial Intelligence

COMMA 2014 conference paper (2014)

Arguments and Their Strength: Revisiting Pollock's Anti-Probabilistic Starting Points

Law, Probability and Risk journal paper (2014)

To Catch a Thief With and Without Numbers: Arguments, Scenarios and Probabilities in Evidential Reasoning

Invited speaker 8th International Workshop on Juris-informatics (JURISIN, Keio University, Tokyo) (2014)

The Future of Argumentation Technology, as guided by the needs of the law

Keynote lecture 9th International Conference on Forensic Inference and Statistics (2014)

To Catch a Thief With and Without Numbers

Artificial Intelligence and Law journal paper (2014)

Building Bayesian Networks for Legal Evidence with Narratives: a Case Study Evaluation(with Charlotte Vlek, Henry Prakken and Silja Renooij)

Stanford event (2014)

Trial With and Without Mathematics. Legal, Philosophical and Computational Perspectives. 2014 Stanford Symposium on Law and Rationality

Invited lecturing Sun Yat-Sen University (2013)

Invited graduate course "Argumentation in Artificial Intelligence, With Applications in the Law" at the Institute of Logic and Cognition, Sun Yat-Sen University, Guangzhou

BNAIC 2013 conference paper (2013)

Inference and Attack in Bayesian Networks (with Sjoerd Timmer, John-Jules Meyer, Henry Prakken and Silja Renooij)

Computational Narrative workshop (2013)

Workshop on Computational Models of Narrative (Hamburg, Germany, August 4-6, 2013), with a paper/presentation by Charlotte Vlek: Representing and Evaluating Legal Narratives with Subscenarios in a Bayesian Network

ICAIL 2013 conference paper (2013)

Modeling Crime Scenarios in a Bayesian Network (with Charlotte Vlek, Henry Prakken, and Silja Renooij)

Artificial Intelligence journal paper (2013)

How Much Does it Help to Know What she Knows you Know? An Agent-Based Simulation Study (with Harmen de Weerd and Rineke Verbrugge)

Program chair (2013)

The Fourteenth International Conference on Artificial Intelligence and Law (ICAIL 2013) Rome, Italy, June 10-14, 2013

AI & Law journal paper (2013)

Legal Stories and the Process of Proof (with Floris Bex)

Journal paper ICAIL@25 (2012)

A history of AI and Law in 50 papers: 25 years of the international conference on AI and Law (with many coauthors; ed. Trevor Bench-Capon)

JELIA conference paper (2012)

Jumping to Conclusions. A Logico-Probabilistic Foundation for Defeasible Rule-Based Arguments

Forensic Science symposium (2012)

1st Symposium NWO Forensic Science (NFI Field Lab, The Hague, September 18, 2012)

Program chair (2012)

The Fourth International Conference on Computational Models of Argument (COMMA 2012) Vienna, Austria, September 10-12, 2012

Argumentation journal paper (2012)

Solving a Murder Case by Asking Critical Questions: An Approach to Fact-Finding in Terms of Argumentation and Story Schemes (with Floris Bex)