By Spoken Chinese, as used in the title of this book, I mean the dialect of Peiping in the middle of the twentieth century, spoken in an informal, sometimes known as casual, style. This gives a general idea of the kind of language we are describing, but as a definition, it is both too wide and too narrow. It is too wide because (a) Peiping is so large that there is noticeable variation, at least in pronunciation, between extreme localities of the city; (b) during the period considered there is already noticeable change in the speech of the same individuals; and (c) even if we specify the style of language studied, there is still considerable variation according to the age group and the social and educational background of the speaker. Strictly speaking, the only thing specifically identifiable is the idiolect of one person at one time. On the other hand, the definition given above is too narrow in that, even if the dialect of Peiping is taken in a broad sense, what is true of that dialect, especially in matters of grammar is usually true of all the northern dialects, and very often true of all the dialects. This is in fact the justification for the ambitious title in which the dialect of Peiping is taken to represent the whole of Spoken Chinese.
 Chao Y R. A grammar of spoken Chinese[M]. Univ of California Press, 1965.