1. Faculty of Law Argumentative Story-based Analysis of Evidence Floris Bex (Law and ICT, U. Groningen) Henry Prakken (Law and ICT, U. Groningen / Information and Computing Sciences, U. Utrecht) Bart Verheij (Artificial Intelligence, U. Groningen)

2. Faculty of Law Contents  Evidential reasoning in legal theory/psychology  Stories (Pennington & Hastie, Crombag et al.)  Argument-graphs (Wigmore, Twining, Schum)  Evidential reasoning in AI (& Law)  Inference to the Best Explanation (Thagard)  Argumentation theory (Prakken, Walton, Gordon)  Combined theory  Example  Conclusions and future research

3. Faculty of Law Stories  Legal decisions are based on stories:  “ sequences of events which form a meaningful whole ”  Stories are compared and the “ best ” story is chosen

4. Faculty of Law Stories  Legal decisions are based on stories:  “ sequences of events which form a meaningful whole ”  Stories are compared and the “ best ” story is chosen  Problem: Relations between evidence, story and generalisations are unclear  Causal relations between events  Sources of evidence

5. Faculty of Law Argument structures  Structured argument-graphs from sources of evidence to conclusion (usually an event)  Generalisations are the “glue” 1234 5678 9 10 Sources of evidence Event to be proven Generalisation (inference warrant)

6. Faculty of Law Argument structures  Structured argument-graphs from sources of evidence to conclusion (usually an event)  Generalisations are the “glue”  Problem: sequence of events unclear  Passage of time  Causal relations between events

7. Faculty of Law Aims  Connect evidence to story using arguments  Formalise the combined theory in order to clarify the different relations event story

8. Faculty of Law Reasoning with evidence in AI (& Law)  Two approaches:  Inference to the Best Explanation (IBE)  Form causal scenarios about “what happened” and compare these scenarios  Argumentation theory  Form arguments from premisses to conclusion

9. Faculty of Law the Rijkbloem case (1)  Nicole Lammers, a baker’s daughter had a relationship with Rijkbloem, a small-time criminal  After breaking up, Nicole and her parents go to Rijkbloem’s house to pick up some of her belongings  A fight develops, which ends in Mr. Lammer’s death

10. Faculty of Law the Rijkbloem case (2)  Fact: Mr. Lammers was shot through the head in Rijkbloem’s house  Prosecution’s story:  The fight between father and Rijkbloem started  Rijkbloem pulled out a gun  Rijkbloem shot father through the head  Father died

11. Faculty of Law the Rijkbloem case (3)  Fact: Mr. Lammers was shot through the head in Rijkbloem’s house  Defence’s story:  The fight between father and Rijkbloem started  Mrs. Lammers pulled a small gun out of her handbag and aimed the gun at Rijkbloem  Rijkbloem tried to push the gun away  The gun accidentally went off  Father was hit in the head and died

12. Faculty of Law IBE – causal reasoning  Stories involve causal reasoning  Stories are (at least) a sequence of events on a timeline  Events are supposedly caused by earlier events  Physical causation  Mental causation

13. Faculty of Law IBE - explanations  Given:  Causal rules T  Facts that need to be explained F  Hypothesise a set of causes H such that the H  T logically implies F (“explains F”) Rijkbloem shoots father Father is hit Father dies Rijkbloem pushes away gun gun goes off Mother pulls out gun

14. Faculty of Law IBE – choice  Choose between the different explanations:

15. Faculty of Law Arguments - evidential reasoning  Reasoning with sources of evidence is evidential  Witness W saying “P” is evidence for P  Gunpowder on Rijkbloem’s hands is evidence for Rijkbloem having fired a gun

16. Faculty of Law Arguments  (formal) argumentation theory Mrs. Lammers says ”Rijkbloem shot my husband!” Rijkbloem shot mr. Lammers If a witness says “P” then usually P

17. Faculty of Law Arguments - attacking  Attacking arguments Rijkbloem says “I did not shoot mr. Lammers!” Rijkbloem did not shoot mr. Lammers Mrs. Lammers says ”Rijkbloem shot my husband!” Rijkbloem shot mr. Lammers If a witness says “P” then usually P

18. Faculty of Law Arguments - attacking  Attacking arguments Mrs. Lammers says ”Rijkbloem shot my husband!” Rijkbloem shot mr. Lammers If a witness says “P” then usually P Mrs. Lammers is not trustworthy

19. Faculty of Law Combining the theories  The stories are modelled as explanations  Sources of evidence are connected to the stories using evidential arguments  Explanations are compared  How much additional evidence is explained?  How much additional evidence is contradicted?  Possible to reason about causal generalisations in the stories

20. Faculty of Law Combining the theories Example Fight Rijkbloem shoots father Father is hit Father dies Police officer’s testimony Forensic report Mrs. Lammers’ testimony Mrs. Lammers is not trustworthy

21. Faculty of Law Combining the theories Example Prosecutions story Defence’s story

22. Faculty of Law Conclusions  Stories and evidence have a seperate place in the theory  Stories and their supporting evidence can be easily combined  Better criteria for comparing stories

23. Faculty of Law Future work  Other criteria for comparing stories  Coherence  Plausibility