The nature of a vital principle is that in which it normally issues. If it issues as a rational substantial form, as in man, it was rational from the beginning. If it was not rational from the beginning, a rational principle replaced a sensory vital principle, and that sensory vital principle replaced a vegetative vital principle. The only reason for these replacements would be that the early human embryo, as has been said, lacks organization sufficient to sustain a form higher than a vegetative principle. If this were sufficient reason for deferring the advent of the rational soul, then a baby six months after birth would have no rational soul because it certainly lacks the supposedly requisite organs. However, as the rational soul is whole in each part of the adult body in the totality of its essence and perfection, but not in the totality of its virtue, because certain organs are lacking in particular parts of the body, it is in the embryo whole in the totality of its essence and perfection, but not in its virtue because certain organs are not yet formed, and it is thus from the moment of conception. As to the soul itself, Kant held that the soul is not a real, but only a logical substance. The Pantheists, Transcendentalists, and Neo-Hegelians try to identify the soul with the divine consciousness. The Associationists (Hume, Davis, Höffding, Sully) say that the soul is a mere group of sensations. The Agnostics and Positivists (Locke, Herbert Spencer, James, Comte) write volume after volume on the soul to prove that they know nothing about it. Then the Materialists assert that there is no soul of any kind; that we secrete thought as a mule secretes sweat. Yet the vital operations of man are inexplicable as resultants of the physical and chemical properties of matter. There is an intrinsic energy that unifies the actions of man, directs processes, controls the tendency of organic matter to pass into the fixity of the inorganic, and effects metabolism. This intrinsic energy is the entelechy, substantial form, or what is popularly called the soul.