Molla Sadra has known the intension of existence and the strength of perceptions as the causes for human soul to grow. In existential aspect, human soul is able to attain all possible grades of existence. On this basis, he divides the grades of human soul into those of plant, animal and human. In this way, human is also divided into angelic and satanic. In perceptional aspect, it is of three grades including natural, mental and intellectual; the grades have been viewed to be in accordance with three worlds of nature, semi-incorporeal and corporeal. In the hereafter, natural human, semi-natural and intellectual men are respectively counted among the left, the right and the elite. Human soul in the grade of intellectual man is equipped with theoretical and practical reason. Sadra has regarded oach of the two reasons to be of four grades.