Language duality is not a problem but an innate ability. It is an accurate
reflection of a duality that exists in all of us, a duality between our
mundane daily life and our spiritual one.
Najīb Maḥfūẓ., Nobel Prize winner for literature 1988,
in a letter to Luwīs ʿAwaḍ.
Although he is referring here to the duality between ECA and MSA – what Ferguson calls diglossia – Maḥ fūẓ. touches upon one of the main functions of language choice. He does not think that duality or bilingualism in general is an impairment.1 In fact, it is an enriching ability that all humans possess and that enables them to express themselves differently and express their diverse needs. He echoes what Myers-Scotton discusses in her book Social motivations for code switching (1993). She refers to code-switching as part of the ‘communicative competence’ of a speaker, which is the competence that individuals acquire from their community and which enables them to communicate effectively with other members of their community. This will be discussed in detail below. Note that Maḥ fūẓ. does not limit ‘language duality’ to a diglossic community or a bilingual one. In this chapter I will discuss code choice and code-switching, whether this code is a variety or a language. After an introduction and discussion of terminology (sections 2.1–2.3), the chapter falls into two main parts. The first part (section 2.4) will examine structural constraints on classic code-switching; switching between different languages, when one of the languages is a variety of Arabic (2.4.1), and diglossic switching as a subcategory of code-switching (2.4.2). I discuss structural constraints on code-switching by examining different theories that can be applied to Arabic. I then provide a case study from my work on structural constraints on diglossic switching as part of code-switching (126.96.36.199). The second part (section 2.5) explains the social motivations and discourse functions of switching