  The importance of Ibn Daud’s psychology does not lie so much in its contents (that are largely based on Ibn Sina’s psychology), but primarily in its detailed treatment and in the manner in which he employs and adapts Ibn Sina’s theories so as to accommodate his own purposes.  The premise that the human soul is an incorporeal substance is the key to the philosophers’ promise that internalizing the intellectual and eternal truths will grant eternal life. The question of immortality is a sophisticated conversion of a theological problem into a philosophical argument regarding the eternity of truth and spiritual pleasures. It is based on Ibn Sina’s discourse on this issue, and in many cases quotes him word for word.