I. Introduction
It can be said that we human beings are a kind of social animals. We do not live in isolation but live in a community. As the member of a community, we have to use our language, the most basic and important medium, to communicate with others. When we speak, we not only produce some units of language with certain meanings, but also make clear our purpose in producing them, the way we intend them to be understood, or they also have certain forces. This is the sense in which to say something is to do something, and the act performed is known as illocutionary act.