# Speech Act Theory as an Evaluation Tool for Human-Agent Communication
## 3 Speech Act Theory  
The meaning of utterance has been defined by many disciplines such as philosophy, linguistics, social sciences, and artificial intelligence. Theories that study the meaning of utterances are called theories of meaning. [PERSON] and [PERSON] [16] present three categories of theories of meaning that influence multi-agent communication formalisms. The first is classical formal semantics, which studies the conditions used to estimate the truth/falsehood of the proposition uttered. The focus of this theory is on linguistic expression and not the relationship between the sender and the receiver or the communication situation. The second theory is intentionalistic semantics, which focuses on what the speaker meant to say in his/her speech. The meaning is conveyed by the speaker's intention. The third theory is the use-theory of meaning, which defines the meaning of language as based on how it is used in the communicative situation.  
Using the foundation of use-theory of meaning, [PERSON] [9] presented Speech Act Theory (SAT). The main idea of SAT is that during communication, people do not just utter propositions to be answered with acceptance or rejection. Instead, every exchanged sentence in a communication situation includes the intention of the speaker to accomplish something such as requesting, advising, and so on. [PERSON] described three characteristics of statements, or acts, that begin with the building blocks of words and end with the effects those words have on an audience.  
1. Locutionary acts: the physical act of uttering the sentence.
2. Illocutionary acts: the action of conveying the speaker's intention, such as informing, ordering, warning, and undertaking.
3. Perlocutionary acts: what we achieve by saying something, such as persuading, convincing, requesting. The perlocutionary effect of an utterance is what is actually achieved by the locution. The perlocutionary effect could be informing of a possible next step, informing of accomplishing a task, persuading someone of my point of view, etc.  
There are different speech act taxonomies for classifying the literal and pragmatic meaning of utterances, such as Verbal Response Modes (VRM) [17] and [PERSON]'s taxonomy. [PERSON]'s taxonomy is more commonly used as his classification covers a wider variety of intentions of utterances. [PERSON] [18] has set up the following classification of illocutionary speech acts:  
* Commissives--speech acts that commit a speaker to performing an action, e.g., promises.
* Declarations--speech acts that bring something about in the world, e.g., pronouncing something.
* Directives--speech acts that influence the listener to take a particular action, e.g., requests, commands, and advice.
* Expressive--speech acts that express the speaker's psychological state or attitudes towards a proposition, and which have an impact on the listener, e.g. congratulations, excuses, and thanking.
* Representatives--speech acts that express the state of the speaker.  
An important assumption of speech act theory is that effective communication requires the accurate recognition of speech acts that are exchanged between players [19].