His theory of human nature is dualistic. Body and Soul have no essential connection with one another. All bodies are produced, under the influence of the stars, from the mingling of the Elements; and in this way the human body also is produced, but from a combination in which the finest proportion is observed. A spontaneous generation of the body, just like the extinction and restoration of the human race, is therefore possible. The Soul, however, is not to be explained from such mixture of the Elements. It is not the inseparable Form of the body, but is accidental to it. From the Giver of Forms, that is—from the Active Spirit over us, every Body receives its own Soul, which is adapted to it and to it alone. From its very beginning each Soul is an individual substance, and it developes increasing individuality throughout its life in the body. It must be admitted that this does not agree with the contention that Matter is the principle of individuality. But the Soul is the “infant prodigy” of our philosopher. He is not a credulous man, and he often cautions us against too ready an acceptance of mysteries in the life of the Soul; but still he has the art himself of relating many things about the numerous wonderful powers and possible influences of the Soul, as it wanders along the highly intricate pathways of life, and crosses the abysses of Being and Not-Being. The speculative faculties are the choicest of all the powers of the Soul. Acquaintance with the world is conveyed to the rational soul by the External and Internal Senses. In particular a full account is given by Ibn Sina of his theory of the Internal Senses, or the sensuous-spiritual faculties of representation, which have their seat in the brain.