 The progress of the soul in this world is through the perfection of intellect that is the life and prime faculty of the soul. Its embodiment facilitates its acquisition of knowledge and the perfection of its intellect but also acts as a cage of restraint. What we see in this passage above is the progression of the soul-intellect through the five stages of the perfection of the intellect described in Avicenna. The soul begins as receptive potentially, then acquires the habit of learning and intellecting until this is perfected; then it is an acquired intellect properly trained. The next stage is the ability of the soul to produce knowledge actively, by being an active intellect; finally it acquires certainty through union with the Active Intellect, a transcendent principle of perfect knowledge which we discuss below. The distinction between the sphere of the intellect and that of the body constitutes a type of dualism that is reflected in Mulla Sadra’s distinction between mental and extra-mental existence. 