View
221
Download
0
Category
Tags:
Preview:
Citation preview
Reasoning with testimony
Argumentation vs. Explanatory Coherence
Floris Bex - University of GroningenHenry Prakken - University of Groningen
- Utrecht University
Introduction
Thagard’s dual pathway model of testimony
Modelling it in our approach (2x) Modelling it in Thagard’s ECHO Comparison
Thagard on testimonies
A claims CC consistent
with my beliefs?A credible?
Accept C
Construct explanatory
network
Does Cmaximize
coherence? Reject C
yes
yesno
no
Default pathway
Reflective pathway
Representing causal knowledge
Explanation with evidential rules:
‘Deduction’:
Explanation with causal rules:
Abduction:
Effect CauseEffect Cause
Cause EffectEffect Cause
Fire causes Smoke
Smoke
Fire
Smoke means Fire
Smoke
Fire
Modelling Thagard’s ideas in our approach (1): both causal and
evidential rules Default pathway: whenever a witness says that P,
believe P (unless …) Can be formalised as argumentation with
evidential rules Causal pathway:
represent all possible causes of the testimony that P: P is true The witness has reason to lie that P His senses deceived him that P His memory deceived him that P …
Then determine the most likely cause Can be modelled as abduction with causal rules
Default pathway R1: Witness W says that P =>e P R2: W has reason to lie that P =>e
exception to R1
… (more exceptions)
Default pathway - example Say that “smoke” is observed (a fact) If we only know that Witness 2 says “smoke
machine”, we can conclude that “smoke machine”
smokemachine
f1: smoke
R1
Witness 2 says “smoke machine”
fire
Default pathway - example
If we also know, that witness 2 has reason to lie about machine, this conclusion is blocked.
smokemachine
f1: smoke
R1
Witness 2 says “smoke machine”
Witness 2 has reason to lie
Default pathway - example What if we have evidence that W
may have reason to lie that machine? => this is where we shift to reflective pathway
smokemachine
f1: smoke
R1
Witness 2 says “smoke machine”
Witness 2 has reason to lie
Reflective pathway
Two explanations for the observations “smoke machine” “fire” and “witness has reason to lie”
f1: smoke
fire
smokemachine
f2: witness says “smoke machine”witness has
reason to lie
Reflective pathway If we also have evidence that W may
have reason to lie, this might create a preference for the “fire-explanation”.
f1: smoke
fire
smokemachine
f2: witness says “smoke machine”witness has
reason to lie
f3
Reflective pathway
But if we have no additional evidence, we have no reason to prefer the “fire- explanation”!
fire & reason to lie
smoke machine
smoke
Intermediate conclusion Our first proposal to model
Thagard’s ideas in our approach requires that a shift from the default to the reflective pathway is modelled as a shift in problem representation Abduction alone cannot justify
believing the witness by default And the truth of P is the usual cause of a
witness statement that P!
Both pathways in argumentation
If we only know that Witness says that P, we can conclude that P
But first we must spend some effort in searching for the exceptions!
smokemachine
f1: smoke
R1
Witness 2 says “smoke machine”
fire
?
?
Principles of coherence
Two propositions A and B cohere iff: A explains B or vice versa (symmetrical) A and B together explain C
Two propositions A and B are in competition iff: A explains C and B explains C They are contradictory
A coherence network
f1: smoke
fire
smokemachine
f2: witness says “smoke machine”witness has
reason to lie
Activation in the network
Activation is between 1 and -1 Evidence nodes (f1…fn) have an
activation of 1 Coherence relation is an excitatory
link Competition relation is an
inhibitory link
Activation in the network
f1: smoke
fire
smokemachine
f2: witness says “smoke machine”witness has
reason to lie
Some comments
Good principles of coherence The “right” result
Not transparent (black box) More complex examples? No modelling of the default
pathway!
A claims C
C consistent with my beliefs?
A credible?
A coherence network needs to be built to answer this question!
Not the only critical question!
Conclusion
In our approach Thagard’s dual pathway model can be modelled as argumentation if embedded in investigation
Thagard only models the reflective pathway
Recommended