1. Argumentation pour le raisonnement pratique
Sylvie DOUTRE
IRIT – Université Toulouse 1

2. Overview Practical reasoning Debate and rational disagreement
Other features of practical reasoning
Positions:
Definition
Construction
Conclusion
S. Doutre
Séminaire IRIT-UT

3. Practical reasoning
Practical reasoning = reasoning about what it is best to do in a given situation
i.e. we have:
alternative actions
reasons to perform or refrain from them, i.e. arguments for and against these actions
 How to reason about these arguments in order to decide what position to adopt?
S. Doutre
Séminaire IRIT-UT

4. Practical reasoning
Example: Hal, a diabetic, loses his insulin and can save his life only by breaking into the house of another diabetic, Carla, and using her insulin.
a. Hal should not take Carla’s insulin as he may be endangering her life.
b. Hal can take the insulin as otherwise he will die, whereas there is only a potential threat to Carla.
c. Hal should not take Carla’s insulin: it is Carla’s property.
d. Hal should replace Carla’s insulin once the emergency is over.
S. Doutre
Séminaire IRIT-UT

5. Debate & rational disagreement
The whole set of arguments relating to an issue (the debate) must be considered
A formalism: [Dung95]
Argument system: pair (X,A) where
X is a set of arguments
A  X x X represents a notion of conflict
Example: b a c d
X = {a,b,c,d}
A = {(b,a), (c,b), (d,c), (b,d)}
S. Doutre
Séminaire IRIT-UT

6. Debate & rational disagreement
[Dung95] (ctd.)
A subset S of arguments is ‘admissible’ if:
Conflict-free (no attack)
Any argument y that attacks an
argument x of S is attacked by an
argument z of S (S defends itself)
Example : x y z S b a c d
 is the only admissible subset according to [Dung95]
S. Doutre
Séminaire IRIT-UT

7. Debate & rational disagreement
Another formalism: [Bench-Capon03]
Value-based argument system: tuple (X, A, V, n) where
(X, A) is a [Dung95] argument system
V is a set of values
n assigns to each argument a value
Example: b a c d
V = { life, property }
n = { (a, life), (b, life), (c, property), (d, property) }
S. Doutre
Séminaire IRIT-UT

8. Debate & rational disagreement
[Bench-Capon03] (ctd.):
Audience = ‘consistant’ ordering of values.
Example: life preferred to property
An argument x defeats an argument y w.r.t. an audience , if:
x attacks y, and
the value of y is not preferred to the value of x according to .
Example: b a c d
Audience 1:
life preferred to property
S. Doutre
Séminaire IRIT-UT

9. Debate & rational disagreement
[Bench-Capon03] (ctd.):
A subset S of arguments is admissible w.r.t. an audience  if:
conflict-free (no defeat)
S defends itself (any defeater of an argument of the set is defeated by the set)
S. Doutre
Séminaire IRIT-UT

10. Debate & rational disagreement
[Bench-Capon03] (ctd.):
Audience 1:
life preferred to property
objectively acceptable b a c d
subjectively acceptable b a c d
Audience 2:
property preferred to life
 Allows rational disagreement
S. Doutre
Séminaire IRIT-UT

11. Other features of practical reasoning
People do not have a conscious understanding of their value preferences independent of the reasoning situations in which they engage [Searle 01].
People are not equally open to all arguments: they may wish to include in or reject some arguments of the positions they construct.
Example: a b
a is ‘desired’
value of a preferred to value of b
Extend [Bench-Capon 03] to take into account 1 and 2.
S. Doutre
Séminaire IRIT-UT

12. Positions: definition
Partitioned Value-based Argument System:
(X, A, V, n) where the set of arguments X is partitioned:
X = Desired U Optional U Rejected
Example:
Desired = { c }
Optional = { b, d }
Rejected = { a } b a c d
S. Doutre
Séminaire IRIT-UT

13. Positions: definition
A subset S of arguments that can be adopted as a position must:
be admissible w.r.t. at least one audience
contain the Desired arguments
contain no Rejected argument
contain as Optional arguments only those that allow S to defend itself
S. Doutre
Séminaire IRIT-UT

14. Positions: definition
Example: b a c d
Desired
Optional
{ c, b } : position?
YES
admissible w.r.t. audience 'life preferred to property', contains the set of Desired arguments, Optional argument b defends c, no rejected argument
{ b, d } : position? NO
admissible w.r.t. audience 'property preferred to life', but it does not contain the set of Desired arguments
S. Doutre
Séminaire IRIT-UT

15. Positions: construction
Procedure:
1. Check that the set of Desired arguments is conflict-free for at least one audience
 May require to impose some value preferences
2. Ensure that any argument defeated is defended
 Use Optional arguments and/or impose some value preferences
 A set of value preferences (an audience) emerges from the construction.
S. Doutre
Séminaire IRIT-UT

16. Positions: construction
In the form of a dialogue between two players:
a proponent:
if the set of Desired arguments is not already a position, then he tries to make it a position by extending it with some Optional arguments and/or some constraints between values
an opponent:
outlines why the set under development is not yet a position
If the one who terminates is:
PRO, then the set of arguments he played is a position, and the set of constraints he played can be extended into a corresponding audience
OPP, then no position contains the desired arguments
S. Doutre
Séminaire IRIT-UT

17. Positions: construction
Example:
PRO: c
OPP: d
PRO: b
OPP: c
PRO: life > property b a c d
 { c, b } is a position w.r.t. the audience 'life preferred to property'
S. Doutre
Séminaire IRIT-UT

18. Positions: construction
Example:
PRO: a
OPP: b
PRO: c
OPP: d b a c d
 Not possible to construct a position containing the set of Desired arguments { a }
S. Doutre
Séminaire IRIT-UT

19. Positions: construction
Heuristics for PRO’s choices:
 keep the extensions of the set under development to a minimum
add an Optional argument that requires no additional value preference
add a new value preference
add an Optional argument that requires an additional value preference but does not conflict with any existing argument
S. Doutre
Séminaire IRIT-UT

20. Conclusion and future work
Practical applications in areas such as:
political debate
case law
Considering extending a debate in which a position has already been constructed: revision of the position
S. Doutre
Séminaire IRIT-UT