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On the structure of arguments, and what it means for dialogue. Henry Prakken COMMA-08 Toulouse, 28-05-2008. Overview. The structure of arguments: overview of state-of-the art Argument schemes A legal example Abstraction in dialogue Combining modes of reasoning Conclusions. - PowerPoint PPT Presentation
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On the structure of arguments, and what it means for dialogue
Henry PrakkenCOMMA-08
Toulouse, 28-05-2008
Overview The structure of arguments: overview of
state-of-the art Argument schemes A legal example
Abstraction in dialogue Combining modes of reasoning
Conclusions
The structure of arguments: current accounts Assumption-based approaches
T = theory A = assumptions, - is conflict relation on A R = inference rules A1 A yields an argument for p if A1 T |-R p A2 for q attacks A1 if q - a for some a A1
Inference-rule approaches T = theory R = inference rules, is conflict relation on R T1 T yields an argument for p if T1|-R p T’2 attacks T1 if T1 applies r1 and T2 applies r2 and
r2 r1
The structure of arguments:An integrated view
Arguments have: Premises
Of various types A conclusion Ways to get from premises to conclusion
Of various types So arguments can be attacked on:
Their premises Some types excluded
Their conclusion The connection between premises and conclusion
Some types excluded
LegalCapacity
Person Exc(R1) R1
“Persons have the capacity to perform legal acts,
unless the law provides otherwise”
LegalCapacity
Person Exc(R1) R1
Minor
Person
R2
< 18
Exc(R1)
LegalCapacity
Person Exc(R1) R1
Minor
Person
R2
< 18
Minor
Person < 18 Married R3
Exc(R1)
Parents know
Parents: “married”
LegalCapacity
Person Exc(R1) R1
Minor
Person
R2
< 18
Minor
Person < 18 Married R3
Exc(R1)
Parents know
Parents: “married”
Biased
Parents Parents are biased
“Undercutters”
Undercutter!
Argument schemes
Many arguments (and attacks) follow patterns Much work in argumentation theory
(Perelman, Toulmin, Walton, ...) Argument schemes Critical questions
Witness testimony(Walton 1996)
Critical questions: Is W really in the position to know about P? Did W really say that P? Is W biased?
Witness W is in the position to now about PW says that P Therefore (presumably), P is the case
Expert testimony(Walton 1996)
Critical questions: Is E a genuine expert on D? Did E really say that P? Is P really within D? Is E biased? Is P consistent with what other experts say? Is P consistent with known evidence?
E is expert on DE says that PP is within D Therefore (presumably), P is the case
From evidence to hypothesis(Walton 1996)
Critical questions: Is it the case that if P is true then Q is true? Has Q been observed? Could there be another reason why Q has been
observed?
If P is the case, then Q will be observed Q has been observedTherefore (presumably), P is the case
What is the logic of argument schemes? (1)
Generalised conditional premise e.g. Katzav & Reed
Defeasible inference rule e.g. me, Gordon(?), Verheij(?)
PremisesIf Premises then typically Conclusion Therefore (presumably), Conclusion
Premises Therefore (presumably), Conclusion
Argumentation schemes in AI
Pollock’s reasons Perception Memory Induction Statistical syllogism Temporal persistence ...
What can be done witharguments in dialogue?
State them (step-by-step or at once) Speech acts for claiming, arguing
Attack them (stating a counterargument)
React to the premises Speech acts for challenging, conceding, retracting, denying statements
React to the inference(?)
Theory building in dialogue In my approach to (persuasion)
dialogue: Agents build a joint theory during the
dialogue An argument graph
Result (ideally) determined by arguments with no challenged or retracted premises
LegalCapacityclaim
LegalCapacityclaim why
LegalCapacity
Person Exc(R1) R1
claim whysince
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
why
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since
concede
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since Minor
Person < 18 Married R3
since
concede
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since Minor
Person < 18 Married R3
since
whyconcede
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since Minor
Person < 18 Married R3
since
why
Parents know
Parents: “married”
since
concede
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since Minor
Person < 18 Married R3
since
why
Parents know
Parents: “married”
since
concede
concede
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since
concede
Minor
Person < 18 Married R3
since
why
Parents know
Parents: “married”
since
concede
Biased
Parents Parents are biased
since
LegalCapacity
Person Exc(R1) R1
Exc(R1)
claim whysince
since
Minor R2
Exc(R1)
Person < 18
why
since
concede
Minor
Person < 18 Married R3
since
why
Parents know
Parents: “married”
since
concede
Biased
Parents Parents are biased
since
why
Reacting to inferences in dialogue
Critical questions of argument schemes: either ask about a premise
covered above or ask about defeaters. Since schemes
are defeasibly valid: Don’t ask the question but state a
counterargument But there is another way of asking
about an inference …
Case study: Murder in a Frisian Boarding House (Floris Bex)
Why?
Why?
Why?
Case study: Murder in a Frisian Boarding House (Floris Bex)
Why?Why?
Abductive reasoning
Louw has a fractured skull
Louw has brain damage
Louw dies
Case study: Murder in a Frisian Boarding House (Floris Bex)
Why?Why?
Why?
Abductive reasoning
Louw has a fractured skull
Louw has brain damage
Louw dies
Louw was hit onthe head by anangular object
Louw fell
Dialogue about abductive model
Louw has a fractured skull
Louw has brain damage
Louw dies
Louw was hit onthe head by anangular object
Louw fell
Why the
facts?
Dialogue about abductive model
Louw has a fractured skull
Louw has brain damage
Louw dies
Louw was hit onthe head by anangular object
Louw fell
(4) Pathologist’sreport
(1) Police report(coroner)
Dialogue about abductive model
Louw has a fractured skull
Louw has brain damage
Louw dies
Louw was hit onthe head by anangular object
Louw fell
(4) Pathologist’sreport
(1) Police report(coroner)
Why the causal
relations?
Dialogue about abductive model
Louw has a fractured skull
Louw has brain damage
Louw dies
Louw was hit onthe head by anangular object
Louw fell
(4) Pathologist’sreport
(1) Police report(coroner)
Case study: Murder in a Frisian Boarding House (Floris Bex)
Why?
Why?
Conclusions from the case study Steps in an argument sometimes
compress complex lines of reasoning Dialogue systems should allow for
‘unpacking’ Sometimes dialogues build theories that
are not argument graphs Sometimes these theories combine
several forms of reasoning A ‘logic’ for such combinations is needed
R1: Kill & Intent MurderR2: Self-defence R1…S hit V, V died from hammer
Murder?
Default logic
R1: Kill & Intent MurderR2: Self-defence R1…S hit V, V died from hammer
Murder?
Default logic
O/I transformers
Causal modelV’s blood on hammerObservations
V died from hammer?
IBE
S hit V?
…..……
R1: Kill & Intent MurderR2: Self-defence R1…S hit V, V died from hammer
Murder?
Default logic
EvidenceCond probsPriors
P(V’s blood on hammer| E)?
Bayesian PT
O/I transformers
Causal modelV’s blood on hammerObservations
V died from hammer?
IBE
S hit V?
…..……
R1: Kill & Intent MurderR2: Self-defence R1…S hit V, V died from hammer
Murder?
Default logic
EvidenceCond probsPriors
P(V’s blood on hammer| E)?
Bayesian PT
Priors?Testimonies
Argumentation
O/I transformers
Ev? CPs?
Causal modelV’s blood on hammerObservations
V died from hammer? S hit V?
…..……
Obs?
CM?
R1: Kill & Intent MurderR2: Self-defence R1…S hit V, V died from hammer
Murder?
EvidenceCond probsPriors
P(V’s blood| E)?
Priors?Testimonies
Procedural law…
Proof standard?
Ev? CPs?
Causal modelV’s blood on hammerObservations
V died from hammer? S hit V?
Obs?
CM?
…..……
EvidenceCond probsPriors’
P(V’s blood| E)?
Causal modelObservations
V died from hammer?
R1: Kill & Intent MurderR2: Self-defence R1…S hit V
Murder?
Final conclusions Inference:
Study the combination of reasoning forms
Be open-minded: don’t force everything into the format of arguments
Dialogue: Allow that argument can be about
something else than arguments Allow for switching between levels of
abstraction
Abduction(Walton 2001)
Critical questions: How good is E in itself as an explanation of F? How much better is E1 than E2,..., En? Are there further findings that change the assessment of E1? Are there further explanations that change the assessment of E?
F is a set of findingsE1, ..., En all explain FE1 best explains F Therefore (presumably), E1 is the case