Overagainst the simplicity of the celestial world we have the sublunary kingdom of the four natures,—the kingdom of contrasts and of change. Even in this realm, in the midst of its plurality, we meet with the unity of an ascending series, from the Elements up to Man. Farabi is unable to advance much that is original on this subject. True to his logical standpoint, he gives himself very little concern about the Natural Sciences, among which, in reliance upon the original unity of matter, he seems without any hesitation to have counted Alchemy. We turn at once to his Doctrine of Man or of the Human Soul, which presents a measure of interest. 9. The powers or divisions of the Human Soul are, in Farabi’s opinion, not of co-ordinate rank, but constitute an ascending series. The lower faculty is Material for the higher; and this again is the Form for the first, while the highest power of all, viz. Thinking, is non-material, and is Form for all the Forms which precede. The life of the Soul is raised from things of sense to thought, by means of the power of Representation; but in all the faculties there is involved Effort or Will. Every theory has its obverse side in practice; and Inclination and Disinclination are inseparable from the perceptions furnished by the senses. To the representations of these the soul takes up an attitude of assent or dissent, by affirming or denying. Finally, Thought passes judgment on Good and Bad, gives to the Will its motives, and constructs Art and Science. All Perception, Representation or Thought is attended with a certain effort to reach the necessary consequence, just as warmth radiates from the substance of fire. The Soul is that which gives completeness (Entelechia) to the existence of the body; but that which gives completeness to the existence of the Soul is the Mind, or the Spirit (ʻaql). The Spirit only is the real Man.