argumentation in artificial intelligence henry prakken lissabon, portugal december 11, 2009

Argumentation in Artificial Intelligence

Henry PrakkenLissabon, Portugal

December 11, 2009

Why do agents need argumentation?

For their internal reasoning To draw conclusions given conflicting arguments

For their interaction with other agents To persuade given a conflict of opinion

Toulmin’s argument scheme

ClaimDataSo

Warrant

Since

Backing

On account of

Rebuttal

Unless

Toulmin’s argument scheme

João is catholicJoão is

Portuguese

So

Most Portugueseare catholic

Since

statistics

On account of

João often visits aprotestant church

Unless

Toulmin’s argument scheme

João is PortugueseJoão was Born

In Portugal

So

Who is born inPortugal isPortuguese

Since

Portuguese law

On account of

João adopted another

nationality

Unless

From Toulmin to modern argumentation theory

Toulmin’s (1958) main contributions: Arguments can be defeated Validity of arguments is procedural (and

field-dependent?) This led to the idea of argument(ation)

schemes. An argument is acceptable if: it instantiates an argument scheme the critical questions asked in dialogue can

be answered

Argument(ation) schemes: general form

But also critical questions

Premise 1, … , Premise nTherefore (presumably), conclusion

Expert testimony(Walton 1996)

Critical questions: Is E really 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

Witness testimony

Critical questions: Is W sincere? Does W’s memory function properly? Did W’s senses function properly?

W says PW was in the position to observe PTherefore (presumably), P

Arguments from consequences

Critical questions: Does A also have bad consequences? Are there other ways to bring about G? ...

Action A brings about G, G is goodTherefore (presumably), A should be done

Three layers in argumentation Logic layer

Fixed theory Procedural layer

Dynamic theory Strategic layer

Dynamic theory

My point: even logic is partly dialectic

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

USA lowered taxes but productivity decreased

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

Prof. P says that …

USA lowered taxes but productivity decreased

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

Prof. P says that …

Prof. P has political ambitions

People with political ambitions are not objective

Prof. P is not objective

USA lowered taxes but productivity decreased

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

Prof. P says that …

Prof. P has political ambitions

People with political ambitions are not objective

Prof. P is not objective

USA lowered taxes but productivity decreased

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

Prof. P says that …

Prof. P has political ambitions

People with political ambitions are not objective

Prof. P is not objective

Increased inequality is good

Increased inequality stimulates competition

Competition is good

USA lowered taxes but productivity decreased

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

Prof. P says that …

Prof. P has political ambitions

People with political ambitions are not objective

Prof. P is not objective

Increased inequality is good

Increased inequality stimulates competition

Competition is good

USA lowered taxes but productivity decreased

A B

C D E

1. An argument is In iff all arguments defeating it are Out.2. An argument is Out iff it is defeated by an argument that is In.

Dung 1995

Grounded semantics minimises node colouring Preferred semantics maximises node colouring

Argument game for grounded semantics

Rules of the game: Proponent starts with an argument Then each player defeats the previous move of the

other player Proponent moves strict defeaters, opponent moves

defeaters Proponent does not repeat his moves

A player wins iff the other player cannot move

Result: A is in the grounded extension iff proponent has a winning strategy in a game about A.

A defeat graph

A

B

C

D

E

F

A game tree

P: AA

B

C

D

E

F

move

A game tree

P: AA

B

C

D

E

F

O: F

move

A game tree

P: AA

B

C

D

E

F

O: F

P: E

move

A game tree

P: A

O: B

A

B

C

D

E

F

O: F

P: E

move

A game tree

P: A

O: B

P: C

A

B

C

D

E

F

O: F

P: E

move

A game tree

P: A

O: B

P: C

O: D

A

B

C

D

E

F

O: F

P: E

move

A game tree

P: A

O: B

P: C P: E

O: D

A

B

C

D

E

F

O: F

P: E

move

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

Prof. P says that …

Prof. P has political ambitions

People with political ambitions are not objective

Prof. P is not objective

Increased inequality is good

Increased inequality stimulates competition

Competition is good

USA lowered taxes but productivity decreased

Structured arguments

Argument structure: Trees where

Nodes are formulas of a logical language L Links are applications of inference rules

Rs = Strict rules (1, ..., 1 ); or Rd= Defeasible rules (1, ..., 1 )

Reasoning starts from a knowledge base K L

Defeat: attack on conclusion, premise or defeasible inference, + preferencesArgument acceptability: Dung (1995)

Argument(ation) schemes: general form

Defeasible inference rules! But also critical questions

Negative answers are counterarguments

Premise 1, … , Premise nTherefore (presumably), conclusion

Expert testimony(Walton 1996)

Critical questions: Is E really 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

We should lower taxes

Lower taxes increase productivity

Increased productivity is good

We should not lower taxes

Lower taxes increase inequality

Increased inequality is bad

Lower taxes do not increase productivity

Prof. P says that …

Prof. P has political ambitions

People with political ambitions are not objective

Prof. P is not objective

Increased inequality is good

Increased inequality stimulates competition

Competition is good

USA lowered taxes but productivity decreased

Three layers in argumentation Logic layer

Fixed theory Procedural layer

Dynamic theory Strategic layer

Dynamic theory

Interaction Argument games verify status of

argument (or statement) given a single theory (knowledge base)

But real argumentation dialogues have Distributed information Dynamics Real players!

A ‘real’ argumentation dialogue I claim that we should lower taxes Why? Since lower taxes increase productivity, which is

good I disagree. We should not lower taxes, since that

would increase inequality, which is bad. Besides, lower taxes will not increase

productivity Why not? Since the USA recently lowered their taxes but

productivity decreased. OK, I admit that lower taxes do not always

increase productivity; I retract my claim.

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 Protocol should promote the goal of the dialogue

Dialogue game systems A communication language

Well-formed utterances Rules for when an utterance is

allowed Protocol

Turntaking rules Termination rules

Dialogical aspects of argument schemes

Some critical questions ask “why this premise?”

Other critical questions ask “is there no exception?” But burden of proof is on respondent to

show that there are exceptions!

Dialogue systems should allow for counterarguments

Need for other speech acts(and for rhetoric)

Paul: r

Olga: s

p qr ps r

Knowledge bases Inference rules

P1: q since p

Need for other speech acts(and for rhetoric)

Paul: r

Olga: s

Knowledge bases Inference rules

P1: q since p

O1: why p?

p qr ps r

Need for other speech acts(and for rhetoric)

Paul: r

Olga: s

Knowledge bases Inference rules

P1: q since p

O1: why p?

P2: p since r

p qr ps r

Need for other speech acts(and for rhetoric)

Paul: r

Olga: s

Knowledge bases Inference rules

P1: q since p

O1: why p?

O2: r since s

P2: p since r

p qr ps r

Some properties that can be studied

Correspondence with participants’ beliefs If union of beliefs implies p, can/will

agreement on p result? If participants agree on p, does union of

beliefs imply p? Disregarding vs. assuming agent

strategies/tactics In general it will be hard to enforce agreement

…

Conclusions Argumentation theory can benefit from AI

Formalisation Computer models Computer tools

AI can benefit from argumentation theory Concepts Theories …