Presentation on Formalising Speech Acts Course:74'757 Formal Logic

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Presentation onFormalising Speech
Acts(Course74.757 Formal Logic)

• Sameer Kumar
• Graduate Student
• Department of Computer Science
• University of Manitoba

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Outline

• Speech Acts
• Formal Model
• Formalising Speech Acts
• Whole Hearted Satisfaction
• Conclusion

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Speech Act Theory

• Speech act theory is important not only in
  Linguistics, but also in Computer Science
• Speech act theory has applications in number of
  areas of Computer Science, including, Distributed
  Computing, Multi-Agent systems, and Natural
  Language Understanding and Generation.

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Multi-Agent Systems (MAS)

• In multi-agent systems, agents interact using
  communication to achieve cooperation and
  coordination with other agents.
• This communication can be studied from the point
  of view of speech act theory.

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What are Speech Acts?

• Speech acts are acts of communication. To
  communicate is to express a certain attitude, and
  the type of speech act being performed
  corresponds to the type of attitude being
  expressed.

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Three kinds of meaning of speech acts

• Locutionary the literal meaning of the utterance
  
• Illocutionary the social function that the
  utterance or written text has (e.g. informing,
  ordering, warning, undertaking.)
• Perlocutionary the result or effect that is
  produced by the utterance in that given context
  (e.g. convincing, persuading, deterring.)

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Illocutionary Vs Perlocutionary

• Ordering someone to do something is
  illocutionary, but getting him to do it is
  perlocutionary. The same sentence may serve as
  both. But the conditions for successful
  perlocutionary acts don't just involve what the
  speaker says, but also its effect on the hearer.

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Kinds of illocutionary acts

• Assertives
• Directives
• Commissives
• Permissives
• Prohibitives
• Declaratives

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Assertives

• Assertives are statements of fact
• These statements may be judged true or false
  because they aim to describe a state of affairs
  in the world.
• Example The door is shut

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Directives

• Directives are commands, requests or suggestions
• These statements attempt to make the other
  person's actions fit the propositional content.
• Example Shut the door

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Commissives

• Commissives are promises
• These are statements, which commit the speaker to
  a course of action as described by the
  propositional content.
• Example I will shut the door

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Permissives

• Permissives issue permission
• These are statements, which allow/permit the
  hearer to a course of action as described by the
  propositional content.
• Example You may shut the door

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Prohibitives

• Prohibitives take the permission away or deny an
  action.
• These are statements, which deny the hearer to a
  course of action as described by the
  propositional content.
• Example You may not shut the door

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Declaratives

• Declaratives entail the occurrence of an action
  in themselves.
• These are statements that attempt to change the
  world by representing it as having been
  changed.
• Example
• I name this door the golden gate
• You are fired

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Parts of Speech Act

• In speech act theory, a speech act is usually
  seen to have two parts an illocutionary force
  and a proposition.
• The illocutionary force distinguishes, e.g., a
  command from a promise
• The proposition describes the state of the world

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Parts of Speech Act

• Speech act illocutionary force and proposition.
• Can be described through a simple formal
  language
• A message, m, is a pair lti,pgt where
• i identifies the illocutionary force and
• p is the proposition.
• i is an atomic symbol from the set assertive,
  directive, commissive, permissive, prohibitive,
  declaratives, and
• p a logical formula.

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Semantics of Speech Acts

• A semantic theory for speech acts is needed to
  provide a rigorous foundation for our
  understanding of languages.
• By semantics of speech acts we mean When does a
  specific speech act occur?, What should happen as
  a result of a speech act? and When is a speech
  act satisfied?
• The presentation specifically focuses on the
  conditions of satisfaction for speech acts.

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Satisfaction of a Speech Act

• The satisfaction of a speech act is very
  different from its being understood
• There are two types of satisfaction Extensional
  and Whole hearted satisfaction
• The extensional satisfaction admits accidental
  success.
• The presentation addresses the whole hearted
  satisfaction (WSAT) where a proposition is not
  only made true, but be made true for sure

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Whole Hearted Satisfaction (WSAT)

• The definition of the satisfaction of speech acts
  as proposed here depends on the definitions of
  know-how and intentions.
• If an agent intends something and persists with
  it and acts on his intention and knows how to
  achieve it, then he will eventually succeed.
• Predicate for intention is intends and two
  predicates for know-how are Khow and Kprev

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Whole Hearted Satisfaction (WSAT)

• intends(x,p) means agent x has intentions to do
  p.
• Khow(x,p) means agent x has the required
  knowledge to achieve p.
• Kprev(x,p) means agent x can prevent p from
  occuring.

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Formal Model

• Each agent influences the future but outcome also
  depends on action of other agents.

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Formal Model

• A scenario at a time is any branch of the future
  beginning there this corresponds to a
  particular run or trace of the given system.
• A sub-scenario is a triple, ltS,t1,t2gt, which
  denotes a section of scenario S from time t1 to
  t2.

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Formal Model

• Let M ltF, gt be an intensional model for
  the language L, where F ltT,lt,fA gt is a frame and
  is an interpretation
• T is a set of all possible times ordered by lt
  and a function, which assigns agents to times,
  fA T ? A (Where A is set of agent symbols)
• assigns intensions (sense, meaning) to
  atomic propositions and to the pairs of agent
  symbols and actions.

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Formal Model

• A scenario at time t is a set S ? T
• St is the class of all scenarios at time t. The
  classes of scenarios at different times are
  disjoint.
• The intension, p, of an atomic proposition p is
  the set of times where it is true.
• t ? p means that p is true at time t
• The intension of an action a is, for each agent
  x, the set of sub-scenarios in the model, in
  which an action a is done by x.
• ltS,t1,t2gt ? ax means that agent x does action a
  in the sub-scenario of S from t1 to t2.

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Formalising Speech Acts

• ltS,t1,t2gt ? says-to(y,m)x
• means that, on scenario S, agent x performed the
  speech act of saying m to agent y in the time
  from t1 to t2
• Comm(x,y,m) is true at scenario S, at time t just
  if x said (or started to say) m to y.

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Semantics of the formal Language

• M ?t p means M satisfies p at time t
• M ?s,t p means M satisfies p at time t on
  scenario S

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Whole Hearted Satisfaction (WHSF) for Assertives

• An assertive is satisfied simply if its
  proposition is true at the time the utterance is
  made.
• Assertive The door is shut is satisfied on all
  scenarios where the door is shut.

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WHSF for Directives

• A directive is satisfied if
• Its proposition, p, becomes true at a point in
  the future of its being said
• All along the scenario from now and then, the
  hearer has the know-how, as well as the intention
  to achieve it.
• A directive to open a door is satisfied if the
  door ends up open, and the hearer continuously
  planned to open the door and was in a position to
  be able to execute the plan to open it

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WHSF for Commissives

• A commisive is satisfied if
• Its proposition, p, becomes true at a point in
  the future of its being said
• All along the scenario from now and then, the
  speaker has the know-how, as well as the
  intention to achieve it
• Technically, a commisive is just like a directive
  except that the role of the hearer is taken over
  by the speaker.

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WHSF for Permissives

• A permissive is satisfied at a scenario and a
  time if it is taken advantage of by the hearer at
  the future point on that scenario
• Hearer can do actions which might possibly have
  led to the condition becoming true
• A permissive allowing a hearer to let the door be
  open is satisfied on a scenario, if the hearer
  can, e.g., risk opening window, even though the
  breeze may open the door
• Without this permissive, the hearer would have to
  take some precaution, e.g., latch the door,
  before opening the door

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WHSF for Prohibitives

• A prohibitive is satisfied at a scenario and time
  if none of the actions done by the hearer on that
  scenario (in the future), can lead to a situation
  where the hearer would be unable to prevent the
  condition from occurring
• A prohibitive to not let the door be open can be
  satisfied only if the hearer does not let the
  window be open, where the opening of the window
  may lead to door being opened

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WHSF for Declaratives

• A declarative is satisfied just if
• Its proposition p becomes true at the time that
  it is said
• All along while the speaker is saying it, he
  intends that condition to occur and knows how to
  make it occur.
• A declarative to name a door the Golden Gate is
  satisfied if the door ends up named thus, and the
  speaker intended it to be so named and knew how
  to name it.

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Verbs of Fulfillment
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Conclusion

• The presentation addressed how speech acts can be
  formalised. Further, it presented a formal model
  for whole hearted satisfaction of speech acts.
• An advantage of this theoretical model approach
  is that it allows our intuitions to be expressed
  directly formally and thus can be used in
  clarifying them.

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References

• Munindar P. Singh, Towards a Formal Theory of
  Communication for Multiagent Systems.
  International Joint Conference on Artificial
  Intelligence (IJCAI), Sydney, Australia, August
  1991
• Munindar P. Singh, A Semantics for Speech Acts.
  Annals of Mathematics and Artificial
  Intelligence, volume 8, number I-II, pages 47-71
  1993
• C. L. Hamblin, Imperatives. Basil Blackwell Ltd.,
  Oxford, UK, 1987
• John L. Austin, How to do Things with Words.
  Clarendon, Oxford, UK, 1962