Download - 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 …