Some of the first studies of the poetry are "Qawa'id al-shi'r" or "The Rules of Poetry" by Tha'lab and "Naqd al-shi'r" "Poetic Criticism" by Qudamah ibn Ja'far. Other works tended to continue the tradition of contrasting two poets in order to determine which one best follows the rule of classical poetic structure. Plagiarism also became a significant idea exercising the critics' concerns. The works of al-Mutanabbi were particularly studied with this concern. He was considered by many the greatest of all Arab poets but his own arrogant self-regard for his abilities did not endear him to other writers and they looked for a source for his verse. Just as there were collections of facts written about many different subjects, numerous collections detailing every possible rhetorical figure used in literature emerged as well as how to write guides.