Two aspects are thus recognizable in the mental interpretation of the environment: on the one hand an aspect which may be called causal, since it seeks the source of the power exerted by Nature forces and objects; on the other, an aspect which is obviously formal, its main significance being that it condenses, so to speak, groups of qualities into a single mental sign. The causal aspect yields, in howsoever simple or complex a form, a theory of the cosmos or of its parts; the formal aspect is no more than a means, ready at hand, in the visible bodies of animals and men for facilitating the use of that theory in processes of thought. Hence we may regard vitalism, animism, psychomorphism as so many stages of man's attitude toward the external system, corresponding with the degree of his power to apprehend the more abstract as distinguished from the more particular and superficial characters of things that come within the range of his knowledge. In the first, he explicitly recognizes vitality, the most obvious character of Nature force; in the second, subsuming vitalism, he raises the soul life to the place of honor; in the third, subsuming both vitalism and animism, he emphasizes in psychomorphism the highest human qualities which his mind enables him to recognize. The passage from the idea of multiplicity to that of unity is itself an inseparable part of the total process. As at the beginning man reads vitality into the separate objects and forces of Nature, without any thought of their underlying unity, so he regards as discrete, unconnected, objectively unrelated, the multifarious souls with which, in his thought, these various powers of the environment have come to be animated. But in course of time, by an inner necessity of intellectual growth, relations come to be perceived between the forces of Nature, likenesses are recognized between the functions of spirits and deities--between the powers put forth and the results achieved. The result is a process of coalescence which, to describe it in the briefest way, first merges a large number of spirit-evolved gods into a smaller number of relatively independent divinities, forms these into pantheons of gods each subordinated to a superior, and finally unites all beings regarded as divine in the single, all-comprehending, omniscient and omnipotent Deity of monotheism.