I will look closely at classic and extended diglossia, diglossia as a continuum, touch upon diglossia within the context of language shift and relationship between diglossia and language varieties. I will incorporate critical opinions of distinguished researchers within the framework of the discussion to provide consistency and comprehensiveness of the analysis and illustrate differences and similarities between diglossia and bilingualism with a number of examples of the way people interact within communities of such countries as Switzerland, Germany, Italy or New Zealand.
Whether diglossia is really a kind of bilingualism is disputed. While a number of researchers categorize diglossia exclusively within the framework of bilingualism, others, to the contrary, treat diglossia and bilingualism as two separate linguistic phenomena in their own right, which tend to overlap each other. In this essay I will touch upon some aspects of diglossia within the context of its relation to bilingualism referring to the studies of the researchers who stress on both similarities and differences between diglossia and bilingualism. According to Charles Ferguson, who first introduced the notion of diglossia into linguistic discourse in 1959, diglossia and bilingualism are closely related notions (Ferguson, 1959). Diglossia is a widespread sociolinguistic phenomenon that applies to a situation within the framework of one speech community, when speakers use two or more language varieties depending on communicative context switching from either local dialect to the literary standard language or vice versa (Ferguson, 1959). For instance, a speaker may use a local dialect of Italian language when communicating to his/her family members at home or friends in informal atmosphere and switch to the literary standard Italian during public speech in formal atmosphere or during a conversation with compatriots from other regions of Italy. It must be noted that according to Ferguson, diglossia is