Argumentation pour le raisonnement pratique Sylvie DOUTRE IRIT – Université Toulouse 1 Sylvie.Doutre@univ-tlse1.fr

Overview Practical reasoning Debate and rational disagreement Other features of practical reasoning Positions: Definition Construction Conclusion S. Doutre Séminaire IRIT-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006

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-UT1 08.06.2006