The aim of this paper is to determine the need of "understanding as a membership of the society" in teaching expository texts. Reading it demand the readers to read with thinking what the writer is trying to say (the third stage) and a selfawareness reading (the fourth stage). The third or fourth stage is based on the theory of the reading phases what Dr. Hirohisa Yoshida has discussed about reading expository texts. When a reader goes on read in the third or fourth stages, it is necessary to recognize "space of the argument" (or the context) that Dr. Hirotaka Nanba has discussed. In reading of expository texts, text or "space of the argument" mean "actual world". The "actual world" is world we live. It is necessary for the readers to conscious that they compose "space of the argument" themselves. The consciousness draws on reader to utilize existing knowledge. In this case, to utilize existing knowledge involve to utilize scientific concepts. To recognize "actual world" in particular, it is efficiently to read expository texts with "social cognizance". To read "space of the argument" with "social cognizance", and to have the consciousness of readers themselves are membership of the space lead to read the text on even ground with the author. In this paper, I describe the reading as "understanding as a membership of the society".