Pragmatics: Speech Acts

Sentences as actions
- Generation as planning to achieve communicative goals
- Understanding as recognition of speaker's plans
Speech act theory (Austin, Searle)
- Types of speech acts: request, inform, promise, etc.
- Speech act independent of the linguistic form which realizes it
  - Where's the post office?
  - Can you tell me where the post office is?
  - You wouldn't happen to know where the post office is, would you?
- Each act defined in terms of the preconditions that need to be satisfed to make it successful and the effect that it has on the hearer
STRIPS-style planning
- Planning knowledge is organized in operators which can add or delete states in the world
- Each operator has preconditions, states which must be true before it can be applied and effects, the addition or deletion of states
- Planning (over-simplified)
  - Given an initial set of states characterizing the world and one or more desired states, find operators with the desired states as effects.
  - Check the preconditions of each selected operator. If the preconditions are satisfied, apply the operator and change the world accordingly (add or delete the effect states). If not, add each unsatisfied precondition to the desired states.
  - Halt when there are no more desired states.

Implementing speech-act theory in a STRIPS-style planner; two over-simplified examples

Request (sp, hr, act)
Preconditions:
  Believe (sp, Cando (hr, act))
  Want (sp, Request (sp, hr, act))
  Channel (sp, hr)
Effect:
  Believe (hr, Want (sp, act))

Inform (sp, hr, prop)
Preconditions:
  Believe (sp, prop)
  Want (sp, Inform (sp, hr, prop)
  Channel (sp, hr)
Effect:
  Believe (hr, Believe (sp, prop))

In order to use these operators in planning, we need two additional operators, which could be assumed to hold in a cooperative, trusting sort of world.

Cause-to-want (agt1, agt2, act)
Preconditions:
  Believe (agt2, Want (agt1, act))
  Believe (agt2, Cando (agt2, act))
Effect:
  Want (agt2, act)

Convince (agt1, agt2, prop)
Precondition:
  Believe (agt2, Believe (agt1, prop))
Effect:
  Believe (agt2, prop)

Example of planning a simple speech act

Initial state:
  Inside (Frank, Room3)
  Believe (Frank, Cando (Frank, Go-Out (Frank, Room3)))
  Believe (Self, Cando (Frank, Go-Out (Frank, Room3)))
  Channel (Self, Frank)

Final state:
  Outside (Frank, Room3)

Selecting Go-Out operator, with bindings
  agt = Frank, src = Room3
Satisfies
  Outside (Frank, Room3)
Has preconditions
  Inside (Frank, Room3) [satisfied]
  Want (Frank, Go-Out (Frank, Room3))

Selecting Cause-to-Want operator, with bindings
  agt1 = Self, agt2 = Frank,
  act = Go-Out (Frank, Room3)
Satisfies
  Want (Frank, Go-Out (Frank, Room 3))
Has preconditions
  Believe (Frank, Want (Self, Go-Out (Frank, Room3)))
  Believe (Frank, Cando (Frank, Go-Out (Frank, Room3)))
     [satisfied]

Selecting Request operator, with bindings
  sp = Self, hr = Frank,
  act = Go-Out (Frank, Room3)
Satisfies
  Believe (Frank, Want (Self, Go-Out (Frank, Room3)))
Has preconditions
  Believe (Self, Cando (Frank, Go-Out (Frank, Room3)))
    [satisfied]
  Channel (Self, Frank) [satisfied]
  Want (Self, Request (Self, Frank, Go-Out (Frank, Room3)))

Assuming the speaker (Self) has control over her own wants,
  she can simply create the new goal
  Want (Self, Request (Self, Frank, Go-Out (Frank, Room3))),
  thus satisfying all of the preconditions

[L645 Syllabus]

Last modified: Thu Dec 11 22:39:02 EST
Comments: gasser@cs.indiana.edu