Abstract: In this paper we discuss the concepts and the functions of the sub je ct and theme of a sentence and their relation. They are the basic concepts in gr ammar and discourse analysis. They are related: subject can be theme and theme is called psychological subject. And they are two different independent concepts with different functions in the discourse: subject realizes the function in prop osition, and theme in message. Subject is to sustain the validity of the stateme nt; and theme is the concern of the message.