Al-Khalil bin Ahmad, born A.D. 718, was one of the great masters in the science of grammar, and the discoverer of the rules of prosody, which art owes to him its creation. He laid the foundation of the language by his book 'Al-Ain' (so called from the letter with which it begins), and by the aid he afforded thereby to Sibawaih, whose master he was, in the composition of his celebrated grammatical work known by the name of 'The Book.' In the work called 'Al-Ain,' Khalil first arranged the stock of Arabic words, dealing with the organ of speech and the production of sounds, and then dividing the words into classes, the roots of which consisted of one, two, three, four, or five letters. It is still a matter of dispute whether the book 'Al-Ain' was wholly composed by Khalil himself, or completed in course of time by his pupils. A copy of this celebrated lexicon and work on philology is in the Escurial Library. Khalil also wrote a treatise on prosody, and other works on grammar, and a book on musical intonation. He died A.D. 786, at Busra. 'Poverty,' he said, 'consists not in the want of money, but of soul; and riches are in the mind, not in the purse.' Sibawaih, the pupil of Khalil, has been called the father of Arabic lexicography, and the lawgiver of Arabic grammar. Ibn Khallikan says that he was a learned grammarian, and surpassed in this science every person of former and later times. As for his 'Kitab,' or 'Book,' composed by him on that subject, it has never had its equal. The great philologist and grammarian, Al-Jahiz, said of the book of Sibawaih, that none like it had ever been written on grammar, and that all writers on this subject who had succeeded him had borrowed from it. When Al-Kisai was tutor to the prince Al-Amin, son of Harun-ar-Rashid, Sibawaih came to Baghdad, and the two great grammarians (Sibawaih, the chief of the school of Busra, and Al-Kisai, chief of the school of Kufa) had a long dispute about a certain expression of Arabic speech, and an Arab of the desert was called in to arbitrate between them. The man first decided in favour of Sibawaih, but when the question was put in another form, the Bedouin asserted that Kisai was right. As Sibawaih considered that he had been unjustly treated in the matter, he left Baghdad for good. The year of his death has been given differently by various authors, the earliest date being A.D. 787, and the latest A.D. 809. The most celebrated grammarians of the third century of the Hijrah (A.D. 816-913) were Al-Mubarrad, who died A.D. 898, and Thalab, who died A.D. 903. They were also great antagonists to each other. Al-Mubarrad, the author of thirty works, was the chief of the school of Busra, and Thalab of that of Kufa, both founded during the preceding century by Sibawaih and Kisai. Thalab was the first collector of books in Islam, and those left by him were very valuable.