same language, usually in different social contexts. This diglossic situation facilitates code-switching in which a speaker switches back and forth between the two dialects of the language, sometimes even within the same sentence. People speak MSA as a third language if they speak other languages native to a country as their first language and colloquial Arabic dialects as their second language. Modern Standard Arabic is also spoken by people of Arab descent outside the Arab world when people of Arab descent speaking different dialects communicate to each other. As there is a prestige or standard dialect of vernacular Arabic, speakers of standard colloquial dialects code-switch between these particular dialects and MSA. Classical Arabic is considered normative; a few contemporary authors attempt (with varying degrees of success) to follow the syntactic and grammatical norms laid down by classical grammarians (such as Sibawayh) and to use the vocabulary defined in classical dictionaries (such as the Lisan al-Arab, ). However, the exigencies of modernity have led to the adoption of numerous terms which would have been mysterious to a classical author, whether taken from other languages (e. g. film) or coined from existing lexical resources (e. g. hātif "caller" > "telephone"). Structural influence from foreign languages or from the vernaculars has also affected Modern Standard Arabic: for example, MSA texts sometimes use the format "A, B, C and D" when listing things, whereas Classical Arabic prefers "A and B and C and D", and subject-initial sentences may be more common in MSA than in Classical Arabic. For these reasons, Modern Standard Arabic is generally treated separately in non-Arab sources. Speakers of Modern Standard Arabic do not always observe the intricate rules of Classical Arabic grammar. Modern Standard Arabic principally differs from Classical Arabic in three areas: lexicon, stylistics, and certain innovations on the periphery that are not strictly regulated by the classical authorities. On the whole, Modern Standard Arabic is not homogeneous; there are authors who write in a style very close to the classical models and others who try to create new stylistic patterns. Add to this regional differences in vocabulary depending upon the influence of the local Arabic varieties and the influences of foreign languages, such as French in Africa and Lebanon or English in Egypt, Jordan, and other countries. As MSA is a revised and simplified form of Classical Arabic, MSA in terms of lexicon omitted the obsolete words used