Commonsense Reasoning and
Argumentation 16/17
HC 13:
Argumentation as dialogue (2) /
Legal argumentation (1)
Henry Prakken
29 March 2017
Contents

Dialogue systems for argumentation (2)


Prakken’s dialogue system framework
Legal argumentation (1)

Classification/interpretation: Factor-based
domains
Two systems for persuasion dialogue

Parsons, Wooldridge & Amgoud


Journal of Logic and Computation 13(2003)
Prakken

Journal of Logic and Computation 15(2005)
Prakken:
languages, logic, agents



Lc: Any, provided it has a reply structure
(attacks + surrenders)
Lt: any
Logic: argumentation logic


 ASPIC+ with grounded semantics
Assumptions on agents: none.
Prakken: example Lc (with
reply structure)
Acts
Attacked by
Surrendered by
claim p
why p
concede p
why p
Argue A
retract p
Argue B
concede A
concede p (p  Prem(A)
(Conc(A) = p)
concede p
retract p
Argue A
(defeats its target)
Why p
Prem(A))
(p 
or p = Conc(A))
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
Termination: if player to move has no legal
moves
…
Outcome: what is dialogical status of initial
move at termination?
Dialogical status of moves

Each move in a dialogue is in or out:


A surrender is out,
An attacker is:

in if surrendered, else:



in iff all its attackers are out
out iff it has an attacker that is in
(An Argue A move is surrendered iff A’s conclusion
is conceded)
Functions of dialogical status

Can determine winning


Proponent wins iff at termination the initial claim is in;
opponent wins otherwise
Can determine turntaking

Turn shifts if dialogical status of initial move has changed


Immediate response protocols
Can be used in defining relevance
1: claim (owe $500)
1: claim (owe $500)
2: why (owe $500)
1: claim (owe $500)
2: why (owe $500)
4: argue (owe $500 since
contract & no payment)
1: claim (owe $500)
2: why (owe $500)
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
1: claim (owe $500)
2: why (owe $500)
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
1: claim (owe $500)
2: why (owe $500)
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
8: argue (contract since notary’s
document & signed by us)
1: claim (owe $500)
2: why (owe $500)
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
8: argue (contract since notary’s
document & signed by us)
11: argue (notary’s document
since notary’s seal is forged)
1: claim (owe $500)
2: why (owe $500)
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
8: argue (contract since notary’s
document & signed by us)
11: argue (notary’s document
since notary’s seal is forged)
12: why (notary’s seal is forged)
1: claim (owe $500)
2: why (owe $500)
13: concede (owe $500))
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
8: argue (contract since notary’s
document & signed by us)
11: argue (notary’s document
since notary’s seal is forged)
12: why (notary’s seal is forged)
Owe 500
contract
signed by us
no payment
notary’s doc
Not notary’s doc
seal forged
Relevant protocols

A reply must be relevant




An attacking move is relevant if it changes the status of the
initial move
A surrendering move is relevant if an attacking counterpart
is relevant
(an attacking counterpart replies to the same move)
The turn shifts if dialogical status of initial move has
changed

Immediate response protocols
P1+
O1P2-
P4+
O2-
O3+
P3+
Relevant target?
P1+
O1P2-
O2+
P3-
O4+
P4+
O3+
P1+
O1P2-
O2-
P3+
P4+
O3+
Relevant target?
P1-
O1+
P2-
O2-
P3+
P4-
O3+
O4+
1: claim (owe $500)
2: why (owe $500)
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
8: argue (contract since notary’s
document & signed by us)
11: argue (notary’s document
since notary’s seal is forged)
12: why (notary’s seal is forged)
What are the relevant
targets for ?
1: claim (owe $500)
2: why (owe $500)
13: concede (owe $500))
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
8: argue (contract since notary’s
document & signed by us)
11: argue (notary’s document
since notary’s seal is forged)
12: why (notary’s seal is forged)
What are the relevant
targets for ?
Game for grounded semantics
unsound in distributed settings
Knowledge bases
Paul: p, r
Olga: s, t
Inference rules
pq
s  q
r  s
r, t  p
P1: q since p
Game for grounded semantics
unsound in distributed settings
Knowledge bases
Paul: p, r
Olga: s, t
Inference rules
pq
s  q
r  s
r,t  p
P1: q since p
O1: q since s
Game for grounded semantics
unsound in distributed settings
Knowledge bases
Paul: p, r
Olga: s,t, r
Inference rules
pq
s  q
r  s
r,t  p
P1: q since p
O1: q since s
P2: s since r
Game for grounded semantics
unsound in distributed settings
Knowledge bases
Paul: p, r
Olga: s,t, r
Inference rules
pq
s  q
r  s
r,t  p
P1: q since p
O1: q since s
P2: s since r
O2: p since r,t
Knowledge bases:
Paul:
p, r,
p ∧r  q,
q s
Olga:
t,
t  p,
p  q
Inference rules:
Rd = {,     }
Rs = all valid inference
rules of prop. l.
No preferences
Acts
Attacked by
Surrendered by
claim p
why p
concede p
why p
Argue A
retract p
Argue B
concede A
concede p (p  Prem(A)
(Conc(A) = p)
concede p
retract p
Argue A
(defeats its target)
Why p
Prem(A))
(p 
or p = Conc(A))
Find a terminated legal dialogue of five
moves with a relevant protocol won by
Olga, assuming both are honest
Winning and logic


A protocol should respect the underlying logic
We want: main claim is in iff it is implied by the
current ‘theory’ of the dialogue


(all non-challenged and non-retracted ‘current’ premises)
Ensured in relevant protocols if



No moves are surrendered; and
Arguments cannot be weakened by ‘backwards extending’
Each argument implied by the current theory has been
moved

Current theory = all non-challenged and non-retractred current
premises
1: claim (owe $500)
2: why (owe $500)
13: concede (owe $500))
4: argue (owe $500 since
contract & no payment)
5: concede (no payment)
6: why (contract)
8: argue (contract since notary’s
document & signed by us)
11: argue (notary’s document
since notary’s seal is forged)
12: why (notary’s seal is forged)
Owe 500
contract
signed by us
no payment
notary’s doc
Not notary’s doc
seal forged
Owe 500
contract
signed by us
no payment
notary’s doc
Not notary’s doc
seal forged
Prakken’s relevant protocols:
characteristics

Protocol





Dialogues



Can be long (stepwise construction of arguments, alternative
replies)
Both sides can develop arguments
Logic



Multiple-move
Multiple-reply
Not deterministic in Lc
Immediate-response
Used for single agent: construct/attack arguments
Used in protocol
Commitments

Not used (could be used in protocol)
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

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!
Example 2
Knowledge bases
Paul:
p
q
Inference rules
Modus ponens
…
Olga:
p
q  p
Paul  Olga does not justify p but they will
agree on p if players are conservative, that
is, if they stick to their beliefs if possible
P1: claim p
Example 2
Knowledge bases
Paul:
p
q
Inference rules
Modus ponens
…
P1: claim p
O1: concede p
Olga:
p
q  p
Paul  Olga does not justify p but they will
agree on p if players are conservative, that
is, if they stick to their beliefs if possible
Example 2
Knowledge bases
Paul:
p
q
Inference rules
Modus ponens
…
P1: claim p
O1: what about q?
Olga:
p
q  p
Possible solution (for open-minded
agents, who are prepared to
critically test their beliefs):
Example 2
Knowledge bases
Paul:
p
q
Inference rules
Modus ponens
…
P1: claim p
O1: what about q?
Olga:
p
q  p
Possible solution (for open-minded
agents, who are prepared to
critically test their beliefs):
P2: claim q
Example 2
Knowledge bases
Paul:
p
q
Inference rules
Modus ponens
…
P1: claim p
O1: what about q?
Olga:
p
q  p
Problem: how to
ensure relevance?
Possible solution (for open-minded
agents, who are prepared to
critically test their beliefs):
P2: claim q
O2: p since q, q  p
Arguing Agents in a MultiAgent System for Regulated
Information Exchange
Pieter Dijkstra
Regulated information exchange


Information exchange is often regulated by
data protection laws
Hardcoding these laws in communication
protocols:



Ensures compliance with the law
But in a rigid way, ignoring exceptional
circumstances, social goals ...
Allow for argumentation
ANITA: MAS for exchanging
crime-related information

Goal of police organisation: exchange as
much information as possible


Goal of crime investigators: protect their
investigation


But stay within the law
Anonymity of informants!
How to balance these goals?


Allow agents to argue with each other;
But also to reason internally about their goals
Example
P: Tell me all you know about recent trading
in explosive materials (request)
P: why don’t you want to tell me?
O: No I won’t (reject)
P: why aren’t you allowed to tell me?
O: since sharing such information could
endanger an investigation
P: You may be right in general (concede) but
in this case there is an exception since
this is a matter of national importance
P: since we have heard about a possible
terrorist attack
P: OK, I agree (offer accepted).
O: since I am not allowed to tell you
O: Why is this a matter of national
importance?
O: I concede that there is an exception, so I
retract that I am not allowed to tell you.
I will tell you on the condition that you
don’t exchange the information with
other police officers (offer)
Example
P: Tell me all you know about recent trading
in explosive materials (request)
P: why don’t you want to tell me?
O: No I won’t (reject)
P: why aren’t you allowed to tell me?
O: since sharing such information could
endanger an investigation
P: You may be right in general (concede) but
in this case there is an exception since
this is a matter of national importance
P: since we have heard about a possible
terrorist attack
P: OK, I agree (offer accepted).
O: since I am not allowed to tell you
O: Why is this a matter of national
importance?
O: I concede that there is an exception, so I
retract that I am not allowed to tell you.
I will tell you on the condition that you
don’t exchange the information with
other police officers (offer)
Example
P: Tell me all you know about recent trading
in explosive materials (request)
P: why don’t you want to tell me?
O: No I won’t (reject)
P: why aren’t you allowed to tell me?
O: since sharing such information could
endanger an investigation
P: You may be right in general (concede) but
in this case there is an exception since
this is a matter of national importance
P: since we have heard about a possible
terrorist attack
P: OK, I agree (offer accepted).
O: since I am not allowed to tell you
O: Why is this a matter of national
importance?
O: I concede that there is an exception, so I
retract that I am not allowed to tell you.
I will tell you on the condition that you
don’t exchange the information with
other police officers (offer)
The communication language
Speech act
Attack
Surrender
request()
offer (’), reject()
-
offer()
offer(’) ( ≠ ’), reject()
accept()
reject()
offer(’) ( ≠ ’),
why-reject ()
-
accept()
-
-
why-reject()
claim (’)
-
claim()
why()
concede()
why()
 since S (an argument)
retract()
 since S
why() (  S)
deny() (  S)
’ since S’ (a defeater)
concede()
concede ’ (’  S)
concede()
-
-
retract()
-
-
deny()
-
-
The protocol





Start with a request
Repy to a previous move of the other agent
Pick your replies from the table
Finish persuasion before resuming negotiation
Turntaking:



In nego: after each move
In pers: various rules possible
Termination:


In nego: if offer is accepted or someone withdraws
In pers: if main claim is retracted or conceded
Example dialogue formalised
P: Request to tell
O: Reject to tell
P: Why reject to tell?
Embedded
persuasion
...
O: Offer to tell if no further exchange
P: Accept after tell no further exchange
Persuasion part formalised
O: Claim Not allowed to tell
P: Why not allowed to tell?
O: Not allowed to tell since telling endangers investigation &
What endangers an investigation is not allowed
P: Concede What endangers an
investigation is not allowed
P: Exception to R1 since National importance
& National importance  Exception to R1
O: Why National importance?
P: National importance since Terrorist threat &
Terrorist threat  National importance
Persuasion part formalised
O: Claim Not allowed to tell
P: Why not allowed to tell?
O: Not allowed to tell since telling endangers investigation &
What endangers an investigation is not allowed
P: Concede What endangers an
investigation is not allowed
P: Concede Exception to R1
P: Exception to R1 since National importance
& National importance  Exception to R1
O: Why National importance?
P: National importance since Terrorist threat &
Terrorist threat  National importance
Persuasion part formalised
O: Claim Not allowed to tell
P: Why not allowed to tell?
O: Not allowed to tell since telling endangers investigation &
What endangers an investigation is not allowed
P: Concede What endangers an
investigation is not allowed
O: Concede Exception to R1
O: Retract
Not allowed to tell
P: Exception to R1 since National importance
& National importance  Exception to R1
O: Why National importance?
P: National importance since Terrorist threat &
Terrorist threat  National importance
Agent Design

Knowledge of




Reasoning


Defeasible
Dialogue policies



Regulations
Goals
Consequences of actions
Negotiation
Persuasion
Belief revision policies
Negotiation policy of
responding agent
Perform requested action?

Obliged?



Forbidden?




yes: accept
no: →
yes: reject
no: →
Violation of own interests?

no: accept

yes: →
Try to find conditions


yes: counteroffer
no: reject
Persuasion policy for
responding agent (1)
How to respond to “p since Q”?

Does the argument satisfy the context criteria?



Does KB imply p?




yes: concede premises and conclusion
no: →
yes: concede conclusion
no: →
Does KB warrant a counterargument (for not-p or an
exception)?

yes: state counterargument

yes or no: →
Investigate each premise q in Q
Persuasion policy for
responding agent (2)
How to respond to premise q of “p since Q”?

Is the argument of the form p since p?



Does KB imply q?



yes: deny p
no: →
yes: concede q
no: →
Does KB imply not-q?

yes: state argument for not-q

no: why q
Persuasion policy for
responding agent (3)
How to respond to “why p”?

Does KB warrant an argument p since Q?


yes: state “p since Q”
no: retract p
Conclusion

We have integrated three strands of
theoretical work on dialogue in a MAS
application scenario:



Argumentation logics
Dialogue systems
Dialogue strategies for agents
Pros and cons at three levels of
legal reasoning

Determining the facts of the case




Classifying the facts under the conditions of a
statutory rule




conflicting sources of evidence
generalisations with exceptions
…
Interpretation rules can have exceptions
conflicting interpretations based on legal principles or values
…
Applying the statutory rule



Conflicting rules
Reasons not to apply the rule
…
Legal reasoning is adversarial


Legal reasoning forms leave room for doubt
Legal cases involve clashes of interest
Dispute

study constructing and attacking arguments
Two topics


Classification/interpretation: Factorbased domains
Interpretation and law making: decision
making
Modelling legal classification and
interpretation in factor-based domains
Running example factors:
misuse of trade secrets

Some factors pro misuse of trade secrets:







F2 Bribe-Employee
F4 Agreed-Not-To-Disclose
F6 Security-Measures
F15 Unique-Product
F18 Identical-Products
F21 Knew-Info-Confidential
Some factors con misuse of trade secrets:




F1 Disclosure-In-Negotiations
F16 Info-Reverse-Engineerable
F23 Waiver-of-Confidentiality
F25 Info-Reverse-Engineered
HYPO
Ashley & Rissland
1985-1990
CATO
Aleven & Ashley
1991-1997
Statistical techniques,
datamining …

Only useful if:





The relevant factors are known
Many precedents are available
The precedents are largely consistent with
each other
Useful for predicting outcomes
But no model of legal reasoning


Black box
No argumentation
66