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He was the first to place consonant-pointing and vowel-pointing (markings) on Arabic letters to clearly identify them. He was the first to write on Arabic linguistics, and is said to be the first to write a book on Arabic grammar (nahw). Al-Du'ali educated many students.
Al-Du'ali is credited with inventing a system of placing large colored dots above certain letters to differentiate consonants (because several groups share the same shape), and indicate short vowels (because the sounds are not otherwise indicated). Consonant differentiation is called I'jam (or naqt). Vowel indication is called tashkil.
Al-Du'ali's large-dot system addressed both of these, resolving readers' confusion and making clear how to read and write Arabic words. Although effective, the large dots were difficult to use on small-size fonts and on any but a limited selection of scripts. They were also time-consuming to make on any size font or script.
Thus, the Umayyad governor al-Hajjaj ibn Yusuf al-Thaqafi asked two of al-Du'ali’s students to create and codify a new system that was simpler and more efficient. A new ‘’tashkil’’ system was developed by Al Khalil ibn Ahmad al-Farahidi (d 786). It has been universally used for Arabic script since the early 11th century.
Ibn al-Nadim, author of the Fihrist said:
"Muhammad b. Ishaq says that most scholars agree that grammar was taken from Abu'l-Aswad al-Du'ali, and that he took it from the Khalifah 'Ali."
This is also the opinion of the famous language specialist Abu 'Ubayda (d 210 AH), and the lexicographer al-Zubaydi (d 397 AH) said about Abu'l-Aswad:
"He was the first to establish the Arabic language, to lay down its methods and to establish its rules."
There are also stories in which both 'Ali and 'Umar acknowledge or refer the subject of grammar to Abu'l-Aswad al-Du'ali. As a consequence, following the order of the governor Ziyad b.
Abi Sufyan, he instructed a scribe, saying:
"When you see me open my mouth at a letter, put a dot above it. When I close it, put one next to the letter. When I draw them apart, put a dot under it."
Another story describes Abu'l-Aswad's reason behind the beginning of grammar.
Some Arabic people laughed once when a client of an Arab mispronounced an Arabic word, so Abu'l-Aswad rebuked them, saying:.
