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.

Henry Prakken

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.

Henry Prakken

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

Henry Prakken

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

Henry Prakken

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

Henry Prakken

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

Henry Prakken

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

Henry Prakken

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 henry@cs.uu.nl 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