Argumentative Storybased Analysis of Evidence Floris Bex 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) 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 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 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 Faculty of Law
Argument structures § Structured argument-graphs from sources of evidence to conclusion (usually an event) § Generalisations are the “glue” 10 Event to be proven 9 5 6 7 8 1 2 3 4 Generalisation (inference warrant) Sources of evidence 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 Faculty of Law
Aims § Connect evidence to story using arguments story event § Formalise the combined theory in order to clarify the different relations 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 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 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 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 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 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 Mother pulls out gun Rijkbloem pushes away gun Father dies gun goes off Faculty of Law
IBE – choice § Choose between the different explanations: 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 Faculty of Law
Arguments § (formal) argumentation theory Rijkbloem shot mr. Lammers If a witness says “P” then usually P Mrs. Lammers says ”Rijkbloem shot my husband!” Faculty of Law
Arguments - attacking § Attacking arguments Rijkbloem did not shoot mr. Lammers Rijkbloem shot mr. Lammers If a witness says “P” then usually P Rijkbloem says “I did not shoot mr. Lammers!” Mrs. Lammers says ”Rijkbloem shot my husband!” Faculty of Law
Arguments - attacking § Attacking arguments Rijkbloem shot mr. Lammers If a witness says “P” then usually P Mrs. Lammers is not trustworthy Mrs. Lammers says ”Rijkbloem shot my husband!” Faculty of Law
Combining 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 Faculty of Law
Combining theories Example Fight Rijkbloem shoots father Father is hit Father dies Mrs. Lammers is not trustworthy Mrs. Lammers’ testimony Forensic report Police officer’s testimony Faculty of Law
Combining theories Example Prosecutions story Defence’s story Faculty of Law
Conclusions § Stories and evidence have a seperate place in theory § Stories and their supporting evidence can be easily combined § Better criteria for comparing stories Faculty of Law
Future work § Other criteria for comparing stories § Coherence § Plausibility Faculty of Law
- Slides: 23