In theology, Al-Hilli was clearly acquainted with the Basran school of Mu'tazilism, as his earliest writing on theology "Manhaj ul-Yaqin fi Usul il-Din", demonstrates. He was also deeply influenced by Nasir al-Din al-Tusi, and wrote a commentary on the latter's famous "Tajrid ul-I'tiqad". This commentary is one of al-Hilli's most widely read works, being the first commentary written on the "Tajrid" and thus forming the basis of later commentators understanding of Tusi's work. Also due to his work in "Tajrid ul-I'tiqad", Al-Hilli has been noted as one of the first Shia Imamiyyah scholars to use the term, "ijtihad" (i’tiqad) in the sense of “putting in of the utmost effort in acquiring the knowledge of the laws of the Shariah”. From this point Shia accepted this term.