INTRODUCTION This chapter attempts to qualify the definition of digraphia in terms of 'form' and 'function', so as to provide a conceptual framework that will allow a broader understanding of the universal nature of writing systems in relation to the social structure in which they are used. Previous studies of digraphia have typically lacked descriptive adequacy. One reason for this has been the fact that language has been considered to be an inexact visual representation of its spoken form. As a result, variations in writing systems have not attracted the same degree of attention as varieties of the spoken language. A second reason has been the fact that the mutual unintelligibility of regional varieties of a spoken language such as Chinese has been ignored, because of a simplistic assumption that people of different dialects experience the same amount of difficulty in learning a phonographic script based on one particular dialect. In fact, people speaking a dialect other than the one on which the phonographic script is based need to make extra efforts to learn the non-native dialect before learning the script. This makes it difficult to perceive the parallelism between digraphia and diglossia, the 'Low' form of which, as defined by Ferguson, is learned as part of the process of acquiring one's mother tongue. Thirdly, intellectual culture, religion and politics have usually been cited as factors underlying the development of digraphia, but, in fact, variation in script has been used for 'membershipping' in very much the same way as spoken varieties have. Taking into account the above points concerning previous approaches to digraphia, I would like to extend the scope of the discussion of this type of linguistic variation by focusing, in this chapter, more directly on the social functions of written language.