Presentation on Formalising Speech Acts (Course:74.757 Formal Logic)

1. Presentation onFormalising Speech Acts(Course:74.757 Formal Logic) Sameer Kumar Graduate Student Department of Computer Science University of Manitoba

2. Outline • Speech Acts • Formal Model • Formalising Speech Acts • Whole Hearted Satisfaction • Conclusion

3. 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.

4. 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.

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

6. 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.)

7. 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.

8. Kinds of illocutionary acts • Assertives • Directives • Commissives • Permissives • Prohibitives • Declaratives

9. 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”

10. 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”

11. 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”

12. 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”

13. 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”

14. 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”

15. 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

16. Parts of Speech Act Speech act: illocutionary force and proposition. Can be described through a simple formal language: A message, m, is a pair <i,p> where • i identifies the illocutionary force and • p is the proposition. • iis an atomic symbol from the set {assertive, directive, commissive, permissive, prohibitive, declaratives}, and • p a logical formula.

17. 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.

18. 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

19. 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’

20. 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.

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

22. 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, <S,t1,t2>, which denotes a section of scenario S from time t1 tot2.

23. Formal Model Let M = 〈F,[ ]〉 be an intensional model for the language L, where F= 〈T,<,fA 〉 is a frame and [ ] is an interpretation T is a set of all possible times ordered by < 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.

24. 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 oftimes 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. • 〈S,t1,t2〉 ∈ [a]x means that agent x does action a in the sub-scenario of S from t1 to t2.

25. Formalising Speech Acts • 〈S,t1,t2〉 ∈ [[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.

26. 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”

27. 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.

28. 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

29. 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.

30. 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

31. 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

32. 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.

33. Verbs of Fulfillment

34. 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.

35. 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