When, after the Muslin conquest, new vernaculars emerged which differed from the language of the Qurʾān, exegetic commentaries became necessary. Grammarians aimed at explaining features in this diglossia within a formal framework. Sībawayhi (eighth century) wrote a fully developed grammar of Arabic which became a highly influential model and included, especially, words analysed in terms of roots, a dependency type of syntax, verb-agent vs. topic-comment sentences.With the spread of Islam, Arabic acquired large numbers of speakers, and grammars of indigenous languages were written — with adaptations — using the Arabic model.