"[2][3] ad-Du'alī is said to have introduced the use of diacritics (consonant and vowel markings) to writing, and to have written the earliest treatises on Arabic linguistics, and grammar (nahw).
ad-Du'ali's large-dot system addressed both of these, resolving readers' confusion and making clear how to read and write Arabic words.
Thus, the Umayyad governor al-Hajjaj ibn Yusuf at-Thaqafi asked two of ad-Duʾali's students to create and codify a new system that was simpler and more efficient.
On four leaves, of what looked to be China paper, in the writing of Yahya ibn Ya'mar, of the Banu Layth was written "Remarks about the Subject and Object".
[12] The Wafayat al-Ayan (Obituaries of Eminent Men) by Ibn Khallikan contains a similar account with additional information: Great diversity of opinion exists about his name, surname and genealogy.
Ali laid down the principle of the three parts of speech; the noun, the verb and the particle and told him to write a treatise on it.
When he noticed that native Arab speech was being influenced by foreign immigrants he asked Ziād to authorize the composition of a guide for correct use.
At first the emir refused but, sometime later overhearing someone say "tuwaffa abāna wa tarak banūn" (which might be rendered in Latin *mortuus est patrem nostrum et reliquit filii, analogous in English to *him died and left they, mistakes due entirely to incorrect vowel choice) - Ziād changed his mind.
Ad-Du'alī's son, Abū Harb, relates that the first section of his father's composition (the art of grammar) was on the "verbs of admiration".
Another account says that it was when he heard a man recite a passage from the Qur'an: Anna ‘llahu bariyon mina ‘l-mushrikina wa rasūluhu, pronounce this last word "rasulihi, that he decided to compose his grammar.
The two titles survived were Ikmāl (completion) that remained then in Fars, and 'al-Jāmī' (the collector), that Sibawaih was in possession of and studying in the course of composing his own treatise, the famous 'Kitab'.