Diglossia is, as far as the Arabic language is concerned, a concept that has been taken for granted, as much as it has been criticized. First, based on Ferguson’s article on diglossia and subsequent interpretations and ramifications of the concept and with a special focus on how language variability is discursively deployed and how it is perceived in the Arab speech community, this article argues that diglossia does not so much describe actual language use, but rather how language variability is ‘read’ in the Arab world. In the second part of the article, an analysis of labeling in a 19th century debate will show how the dichotomy between fuṣḥā and non-fuṣḥā varieties (ʿāmmīya),1 which is the basis of diglossia, was already taken for granted long before the concept and the term existed, and even before fuṣḥā and ʿāmmīya were used as independent lexical items. The analysis in both parts of the article shows how much diglossia is taken for granted by most native speakers of Arabic, even if it defies linguistic descriptions of actual language use. It is exactly this ‘common-sense-ness’ that suggests that diglossia is a useful tool to describe language ideological attitudes.