Although he is referring here to the duality between ECA and MSA – what Ferguson calls diglossia – Maḥfūẓ touches upon one of the main functions of language choice. He does not think that duality or bilingualism in general is an impairment. 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 Maḥfūẓ 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.