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)
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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
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Stories
Legal decisions are based on stories: “sequences of events which form a meaningful whole”
Stories are compared and the “best” story is chosen
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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
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Argument structures
Structured argument-graphs from sources of evidence to conclusion (usually an event)
Generalisations are the “glue”
1 2 3 4
5 6 7 8
9
10
Sources of evidence
Event to be proven
Generalisation (inference warrant)
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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
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Aims
Connect evidence to story using arguments
Formalise the combined theory in order to clarify the different relations
event eventeventevent
story
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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
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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
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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
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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
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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
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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 pullsout gun
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IBE – choice
Choose between the different explanations:
Father dies
Prosecution’s explanation
Defence’s explanation
choice
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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
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Arguments
(formal) argumentation theory
Mrs. Lammers says ”Rijkbloem shot my
husband!”
Rijkbloem shot mr. Lammers
If a witness says “P” then usually P
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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
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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
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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
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Combining the theoriesExample
FightRijkbloem
shoots father
Father is hit
Father dies
Police officer’s testimony
Forensic report
Mrs. Lammers’ testimony
Mrs. Lammers is not trustworthy
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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