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Published on January 23, 2008

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Argumentation in Agent Systems Part 2: Dialogue :  Argumentation in Agent Systems Part 2: Dialogue Henry Prakken EASSS-07 31-08-2007 Why study argumentation in agent technology?:  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 Overview:  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 Argument schemes: general form:  Argument schemes: general form The same as logical inference rules But also critical questions Pointers to undercutters Premise 1, … , Premise n Therefore (presumably), conclusion Statistical syllogism :  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 “Normative syllogism” :  “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 Witness testimony:  Witness testimony Critical questions: Is W sincere? (veracity) Did W really see P? (objectivity) Did P occur? (observational sensitivity) Witness W says P Therefore (presumably), P Temporal persistence:  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 > T1 Therefore (presumably), P is Still true at T2 Arguments from consequences:  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 consequences Therefore (presumably), A should be done Types of dialogues (Walton & Krabbe):  Types of dialogues (Walton & Krabbe) Example :  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 good O: since French cars are unsafe O: since magazine Meinwagen says so O: 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. Example (2) :  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 good O: since French cars are unsafe O: since magazine Meinwagen says so O: 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. Example (3) :  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 good O: since French cars are unsafe O: since magazine Meinwagen says so O: 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. Dialogue systems (according to Carlson 1983):  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 Dialogue game systems:  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 Some history:  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 Persuasion:  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, … Information seeking:  Information seeking Dialogue goal: information exchange Agent’s goals: learning(?) Typical speech acts: Ask p, Tell p, Notell p, … Negotiation:  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, … Deliberation:  Deliberation Participants: any Dialogue goal: resolve need for action Participants’ goals: None initially Possible set of speech acts: Propose, ask-justify, prefer, accept, reject, … Dialectical shifts to persuasion:  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 Commitment in dialogue:  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 Quality aspects of dialogue protocols:  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? Effectiveness vs fairness :  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, … Public semantics: Commitments in persuasion:  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” Assertion/Acceptance attitudes:  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! Two systems for persuasion dialogue:  Two systems for persuasion dialogue Parsons, Wooldridge & Amgoud Journal of Logic and Computation 13(2003) Prakken Journal of Logic and Computation 15(2005) PWA: languages, logic, agents:  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 PWA: protocol:  PWA: protocol W claims p; B concedes if allowed, if not claims p if allowed or else challenges p If B claims p, then goto 2 with players’ roles reversed and p in place of p; If B has challenged, then: W claims S, an argument for p; Goto 2 for each s  S in turn. B concedes if allowed, or the dialogue terminates. Outcome: do players agree at termination? Slide30:  P1: My car is safe. claim P2: 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? challenge O2: That is true, concession but your car is still not safe counterclaim O3: 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 PWA: example dialogue:  PWA: example dialogue P: careful/cautious P1: claim safe P2: claim {airbag, airbag  safe} P3: claim {airbag  safe} O: thoughtful/cautious O1: why safe O2a: concede airbag O2b: why airbag  safe P: careful/cautious P1: claim safe. P2: why safe P3a: concede newspaper P3b: why newspaper   safe O: confident/cautious O1: claim safe O2: claim {newspaper, newspaper   safe} O3: claim {newspaper   safe} PWA: characteristics:  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 Prakken: languages, logic, agents:  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. Prakken: example Lc (with reply structure):  Prakken: example Lc (with reply structure) Protocol variations:  Protocol variations Unique-vs multiple moves per turn Unique vs. multiple replies Immediate response or not … Prakken: protocols (basic rules):  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? Dialogical status of moves:  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 Slide38:  P1+ O1- P2- P4+ O2- O3+ P3+ Functions of dialogical status:  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 Relevant protocols:  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 Slide41:  P1+ O1- P2- P4+ O2- O3+ P3+ Slide42:  P1+ O1- P2- P4+ O2+ O3+ P3- O4+ Slide43:  P1+ O1- P2- P4+ O2- O3+ P3+ Slide44:  P1- O1+ P2- P4- O2- O3+ P3+ O4+ Prakken: example dialogue:  Prakken: example dialogue P1: claim safe Prakken: example dialogue:  Prakken: example dialogue P1: claim safe O1: why safe Prakken: example dialogue:  Prakken: example dialogue P1: claim safe O1: why safe P2: safe since airbag, airbag  safe Prakken: example dialogue:  Prakken: example dialogue P1: claim safe O1: why safe P2: safe since airbag, airbag  safe O2a: concede airbag Prakken: example dialogue:  Prakken: example dialogue P1: claim safe O1: why safe P2: safe since airbag, airbag  safe O2a: concede airbag O2b: safe since newspaper, newspaper  safe Prakken: example dialogue:  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 Prakken: example dialogue:  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 Prakken: example dialogue:  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 Prakken: example dialogue:  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 Argument graph:  Argument graph so what unreliable unreliable  so what Winning and logic:  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) Prakken’s relevant protocols: characteristics:  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 Filibustering:  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? ... Possible sanctions:  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! Protocol design vs. agent design:  Protocol design vs. agent design Can protocol designer rely on agent properties? Rationality Cooperativeness Social behaviour Design of dialogical agents:  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 Investigation of protocol properties (formal proof of experimentation):  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? Research issues:  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 … Further reading:  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

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