Reconstruction of the idea of "Aṣl" from the viewpoint of Shaykh Ṭūsī

"Aṣl" as the most pivotal traditional manuscript has played a key role in forming the collections of Imami Hadith throughout the history of Shia. That is why Shiite scholars have always attempted to identify this concept clearly, and then recognize its instances. Although Shaykh Ṭūsī made lots of efforts to present "Uṣūl" to next generations, but his viewpoint about this genre of traditional manuscript is not clear to us. This study tries for the first time to explain his attitude towards "Aṣl" throughout paying attention to his accounts of this concept. This study shows that Shaykh Ṭūsī, confining authors of "Uṣūl" to disciples of Imam Sadiq(a.s), identified the concept of "Aṣl" in the contrary of "Muṣannaf". According to this, "Aṣl" is a traditional manuscript which contains just the teachings of Imam(a.s) without classification and author's personal views. In addition, this study explains the sources by which Shaykh Ṭūsī recognized "Uṣūl".