Argumentation Logics Lecture 3: Abstract argumentation preferred semantics
Argumentation in Agent Systems Part 2: Dialogue
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Transcript of Argumentation in Agent Systems Part 2: Dialogue
Argumentation in Agent SystemsPart 2:
Dialogue
Henry PrakkenEASSS-07
31-08-2007
Henry Prakken
Why study argumentation in agent technology?
For internal reasoning of single agents Reasoning about beliefs, goals, intentions
etc often is defeasible For interaction between multiple agents
Information exchange involves explanation Collaboration and negotiation involve
conflict of opinion and persuasion
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Overview Recent trends in argumentation logics
Argument schemes Epistemic vs. practical reasoning
Argumentation in dialogue Dialogue game approach Types of dialogues
How they involve argumentation The notion of commitment
Some dialogue systems Agent behaviour in dialogues Research issues
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Argument schemes: general form
The same as logical inference rules
But also critical questions Pointers to undercutters
Premise 1, … , Premise nTherefore (presumably), conclusion
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Statistical syllogism
P and if P then usually Q is a reason to believe that Q
Birds usually fly Critical question: subproperty
defeater? Conflicting generalisation about an
exceptional class Penguins don’t fly
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“Normative syllogism” P and if P then as a rule Q is a reason to
accept that Q Critical question: are there exceptions?
How does a lawyer argue for exceptions to a rule?
Say legislation makes an exception Say it is motivated by the rule’s purpose Find an overruling principle Argue that rule application has bad consequences
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Witness testimony
Critical questions: Is W sincere? (veracity) Did W really see P? (objectivity) Did P occur? (observational sensitivity)
Witness W says PTherefore (presumably), P
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Temporal persistence
Critical questions: Was P known to be false between T1
and T2? Is the gap between T1 and T2 too long?
P is true at T1 and T2 > T1Therefore (presumably), P isStill true at T2
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Arguments from consequences
Critical questions: Does A also have bad consequences? Are there other ways to bring about the
good consequences?
Action A brings about good consequencesTherefore (presumably), A should be done
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Types of dialogues (Walton & Krabbe)
Dialogue Type Dialogue Goal Initial situation
Persuasion resolution of conflict conflict of opinion
Negotiation making a deal conflict of interest
Deliberation reaching a decision need for action
Information seeking
exchange of information
personal ignorance
Inquiry growth of knowledge general ignorance
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Example P: I offer you this Peugeot for $10000.P: why do you reject my offer?P: why are French cars no good?P: why are French cars unsafe?P: Meinwagen is biased since German
car magazines usually are biased against French cars
P: why does Meinwagen have a very high reputation?.
P: OK, I accept your offer.
O: I reject your offer
O: since French cars are no goodO: since French cars are unsafeO: since magazine Meinwagen says
soO: I concede that German car
magazines usually are biased against French cars, but Meinwagen is not since it has a very high reputation.
O: OK, I retract that French cars are no good. Still I cannot pay $10.000; I offer $8.000.
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Example (2) P: I offer you this Peugeot for $10000.P: why do you reject my offer?P: why are French cars no good?P: why are French cars unsafe?P: Meinwagen is biased since German
car magazines usually are biased against French cars
P: why does Meinwagen have a very high reputation?.
P: OK, I accept your offer.
O: I reject your offer
O: since French cars are no goodO: since French cars are unsafeO: since magazine Meinwagen says
soO: I concede that German car
magazines usually are biased against French cars, but Meinwagen is not since it has a very high reputation.
O: OK, I retract that French cars are no good. Still I cannot pay $10.000; I offer $8.000.
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Example (3) P: I offer you this Peugeot for $10000.P: why do you reject my offer?P: why are French cars no good?P: why are French cars unsafe?P: Meinwagen is biased since German
car magazines usually are biased against French cars
P: why does Meinwagen have a very high reputation?.
P: OK, I accept your offer.
O: I reject your offer
O: since French cars are no goodO: since French cars are unsafeO: since magazine Meinwagen says
soO: I concede that German car
magazines usually are biased against French cars, but Meinwagen is not since it has a very high reputation.
O: OK, I retract that French cars are no good. Still I cannot pay $10.000; I offer $8.000.
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Dialogue systems (according to Carlson 1983)
Dialogue systems define the conditions under which an utterance is appropriate
An utterance is appropriate if it furthers the goal of the dialogue in which it is made
Appropriateness defined not at speech act level but at dialogue level
Dialogue game approach
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Dialogue game systems A dialogue purpose Participants (with roles) A communication language Lc
With embedded topic language Lt and a logic for Lt
A protocol for Lc Effect rules for Lc (“commitment
rules”) Termination and outcome rules
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Some history In philosophy: formal dialectics
(Hamblin 1970, MacKenzie 1979, Walton & Krabbe 1995, …) Deductive setting
In AI: procedural defeasibility Loui (1998(1992)), Brewka (1994,2001) Adding counterarguments
In AI & Law: dispute resolution (Gordon 1993, Bench-Capon 1998, Lodder 1999, Prakken 2000-
2006, …) Adding counterarguments and third parties
In MAS: agent interaction Parsons-Sierra-Jennings 1998, Amgoud-Maudet-Parsons 2000,
McBurney-Parsons 2002, … Adding agents
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Persuasion Participants: proponent (P) and opponent
(O) of a dialogue topic t Dialogue goal: resolve the conflict of
opinion on t. Participants’ goals:
P wants O to accept t O wants P to give up t
Typical speech acts: Claim p, Concede p, retract p, Why p, p since
S, …
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Information seeking Dialogue goal: information
exchange Agent’s goals: learning(?) Typical speech acts:
Ask p, Tell p, Notell p, …
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Negotiation Dialogue goal: agreement on
reallocation of scarce resources Participants’ goals: maximise
individual gain Typical communication language:
Request p, Offer p, Accept p, Reject p, …
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Deliberation Participants: any Dialogue goal: resolve need for
action Participants’ goals:
None initially Possible set of speech acts:
Propose, ask-justify, prefer, accept, reject, …
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Dialectical shifts to persuasion
Information exchange: explaining why something is the case or how I know it Persuasion over fact
Negotiation: explaining why offer is good for you or bad for me Persuasion over fact or action
Deliberation: explaining why proposal is good or bad for us Persuasion over fact or action
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Commitment in dialogue Walton & Krabbe (1995):
General case: commitment to action Special cases:
Commitment to action in dialogue (dialogical or propositional commitment)
Commitment to action outside dialogue (social commitment)
Negotiation and deliberation lead to social commitments
Persuasion leads to dialogical commitments
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Quality aspects of dialogue protocols
Effectiveness: does the protocol further the dialogue goal? Commitments Agents’ logical and dialogical consistency Efficiency (relevance, termination, ...)
Fairness: does the protocol respect the participants’ goals? Flexibility, opportunity, …
Public semantics: can protocol compliance be externally observed?
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Effectiveness vs fairness Relevance and efficiency: moves
should be related to the dialogue topic
Relevance often enforced in rigid so efficient “unique-move immediate response” protocols
But sometimes participants must have freedom to backtrack, to explore alternatives, to postpone responses, …
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Public semantics:Commitments in persuasion
A participant’s publicly declared standpoints, so not the same as beliefs!
Only commitments and dialogical behaviour should count for move legality: “Claim p is allowed only if you believe p” vs. “Claim p is allowed only if you are not
committed to p and have not challenged p”
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Assertion/Acceptance attitudes
Relative to speaker’s own knowledge! Confident/Thoughtful agent: can assert/accept
P iff he can construct an argument for P Careful/cautious agent: can assert/accept P iff
he can construct an argument for P and no stronger counterargument
Thoughtful/skeptical agent: can assert/accept P iff he can construct a justified argument for P
If part of protocol, then protocol has no public semantics!
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Two systems for persuasion dialogue Parsons, Wooldridge & Amgoud
Journal of Logic and Computation 13(2003)
Prakken Journal of Logic and Computation
15(2005)
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PWA: languages, logic, agents
Lc: Claim p, Why p, Concede p, Claim S, Question p p Lt, S Lt
Lt: propositional Logic: argumentation logic
Arguments: (S, p) such that S Lt, consistent S propositionally implies p
Attack: (S, p) attacks (S’, p’) iff p S’ and level(S) ≤ level(S’)
Semantics: grounded Assumptions on agents:
Have a knowledge base KB Lt Have an assertion and acceptance attitude
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PWA: protocol1. W claims p;2. B concedes if allowed, if not claims p if
allowed or else challenges p3. If B claims p, then goto 2 with players’ roles
reversed and p in place of p;4. If B has challenged, then:
1. W claims S, an argument for p;2. Goto 2 for each s S in turn.
5. B concedes if allowed, or the dialogue terminates.
Outcome: do players agree at termination?
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P1: My car is safe. claimP2: Since it has an airbag. argument
P3: why does that not make my car safe? challenge
P4: Yes, that is what the newspapers say, concession but that does not prove anything, since newspapers are unreliable sources of technological information undercutter
P5: OK, I was wrong that my car is safe. retraction
O1: Why is your car safe? challengeO2: That is true, concession but your
car is still not safe counterclaimO3: Since the newspapers recently
reported on airbags exploding without cause rebuttal
O4: Still your car is not safe, since its maximum speed is very high. alternative rebuttal
Example persuasion dialogue
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PWA: example dialogueP: careful/cautiousP1: claim safe P2: claim {airbag, airbag safe}
P3: claim {airbag safe}
O: thoughtful/cautiousO1: why safeO2a: concede airbagO2b: why airbag safe
P: careful/cautiousP1: claim safe. P2: why safe
P3a: concede newspaperP3b: why newspaper safe
O: confident/cautiousO1: claim safeO2: claim {newspaper, newspaper safe}
O3: claim {newspaper safe}
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PWA: characteristics Protocol
multi-move (almost) unique-reply Deterministic in Lc
Dialogues Short (no stepwise construction of arguments, no
alternative replies) Only one side develops arguments
Logic used for single agent: check attitudes and
construct argument
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Prakken: languages, logic, agents
Lc: Any, provided it has a reply structure (attacks + surrenders)
Lt: any Logic: argumentation logic
Arguments: trees of conclusive and/or defeasible inferences
Attack: depends on chosen logic Semantics: grounded
Assumptions on agents: none.
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Prakken: example Lc (with reply structure)
Acts Attacked by
Surrendered by
claim p why p concede p
why p p since S retract p
concede p
retract p
p since S p’ since S’why s (s S)
concede (p since S)concede s (s S)
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Protocol variations Unique-vs multiple moves per turn Unique vs. multiple replies Immediate response or not …
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Prakken: protocols (basic rules)
Each noninitial move replies to some previous move of hearer
Replying moves must be defined in Lc as a reply to their target
Argue moves must respect underlying argumentation logic
Termination: if player to move has no legal moves
Outcome: what is dialogical status of initial move at termination?
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Dialogical status of moves Each move in a dialogue is in or
out: A surrender is out, An attacker is:
in iff surrendered, else: in iff all its attacking children are out
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P1+
O1-
P2- P4+
O2- O3+
P3+
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Functions of dialogical status Can determine winning
Plaintiff wins iff at termination the initial claim is in; defendant wins otherwise
Can determine turntaking Turn shifts if dialogical status of initial move
has changed Immediate response protocols (Loui 1998)
Can be used in defining relevance
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Relevant protocols
A move must reply to a relevant target A target is relevant if changing its
status changes the status of the initial claim
Turn shifts if dialogical status of initial move has changed Immediate response protocols
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P1+
O1-
P2- P4+
O2- O3+
P3+
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P1+
O1-
P2- P4+
O2+ O3+
P3-
O4+
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P1+
O1-
P2- P4+
O2- O3+
P3+
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P1-
O1+
P2- P4-
O2- O3+
P3+
O4+
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Prakken: example dialogue
P1: claim safe
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Prakken: example dialogue
P1: claim safe
O1: why safe
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Prakken: example dialogue
P1: claim safe
O1: why safe
P2: safe since airbag,airbag safe
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Prakken: example dialogue
P1: claim safe
O1: why safe
P2: safe since airbag,airbag safe
O2a: concede airbag
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Prakken: example dialogue
P1: claim safe
O1: why safe
P2: safe since airbag,airbag safe
O2a: concede airbag O2b: safe since newspaper, newspaper safe
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Prakken: example dialogue
P1: claim safe
O1: why safe
P2: safe since airbag,airbag safe
O2a: concede airbag O2b: safe since newspaper, newspaper safe
P3a: concede newspaper
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Prakken: example dialogue
P1: claim safe
O1: why safe
P2: safe since airbag,airbag safe
O2a: concede airbag O2b: safe since newspaper, newspaper safe
P3a: concede newspaper P3b: so what since unreliable, unreliable so what
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Prakken: example dialogue
P1: claim safe
O1: why safe
P2: safe since airbag,airbag safe
O2a: concede airbag O2b: safe since newspaper, newspaper safe
O3: safe since high speed, high speed safe
P3a: concede newspaper P3b: so what since unreliable, unreliable so what
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Prakken: example dialogue
P1: claim safe
O1: why safe
P2: safe since airbag,airbag safe
O2a: concede airbag O2b: safe since newspaper, newspaper safe
O3: safe since high speed, high speed safe
P3a: concede newspaper P3b: so what since unreliable, unreliable so what
P4: retract safe
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Argument graph
safe
airbag airbag safe
safe
newspaper newspaper safe
safe
high speed high speed safe
so what
unreliable unreliable so what
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Winning and logic A protocol should respect the
underlying logic We want: main claim is in iff it is
implied by the exchanged information (except information that is disputed
and not defended) Ensured in relevant protocols (under
certain conditions)
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Prakken’s relevant protocols: characteristics
Protocol Multiple-move Multiple-reply Not deterministic in Lc Immediate-response
Dialogues Can be long (stepwise construction of arguments,
alternative replies Both sides can develop arguments
Logic Used for single agent: construct/attack arguments Used for outcome: players jointly build dialectical graph
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Filibustering Many two-party protocols allow
obstructive behaviour: P: claim p O: why p? P: p since q O: why q? P: q since r O: why r? ...
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Possible sanctions Social sanctions:
I don’t talk to you any more Shift of burden of proof by third
party ... P: q since r O: why r? referee: O, you must defend not-r!
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Protocol design vs. agent design Can protocol designer rely on
agent properties? Rationality Cooperativeness Social behaviour
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Design of dialogical agents Assertion and acceptance attitudes
(PWA) Model choice of move as planning /
practical reasoning Amgoud 2006
Apply game theory Roth 2007
Much work remains to be done
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Investigation of protocol properties(formal proof of experimentation) Does protocol induce “well-behaved” dialogues?
(is it fair and effective?) Do agent attitudes, external goals or social
conventions induce “well-behaved” dialogues? If a claim is successfully defended, is it implied by
The shared or joint commitments of all participants? The shared or joint beliefs of all participants? …
Do agent attitudes constrain or even predetermine the outcome?
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Research issues Investigation of protocol properties Combinations of dialogue types
Deliberation! Multi-party dialogues Protocol design vs agent design Embedding in social context A framework for dialogue games …
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Further reading Argumentation in logic
H. Prakken & G. Vreeswijk, Logics for defeasible argumentation (Handbook of Philosophical Logic, 2nd edition)
Mail [email protected] for a pdf copy Argumentation in dialogue
H. Prakken, Formal systems for persuasion dialogue. The Knowledge Engineering Review 21:163-188, 2006.
I. Rahwan et al., Argumentation-based negotiation, The Knowledge Engineering Review 18:343-375, 2003.
For more resources see: http://www.cs.uu.nl/people/henry/easss07.html