From the study of the development of human intelligence, in all directions, and through all times, the discovery arises of a great fundamental law, to which it is necessarily subject, and which has a solid foundation of proof, both in the facts of our organization and in our historical experience. This law is this: that each of our leading conceptions--each branch of our knowledge--passes successively through three different theoretical conditions: the theological, or fictitious; the metaphysical, or abstract; and the scientific, or positive. In other words, the human mind, by its nature, employs in its progress three methods of philosophizing, the character of which is essentially different and radically opposed: viz., the theological method, the metaphysical and the positive. Hence arise three philosophies, or general systems of conceptions on the aggregate of phenomena, each of which excludes the others. The first is the necessary point of departure of the human understanding; the third is its fixed and definite state. The second is merely a state of transition. In order for a man who has reached the scientific stage in his intellectual development to make anything out of the reasonings of those who are still in the stage of theological childhood or in that of metaphysical adolescence, it is necessary for him to use their insubstantialities as symbols of his substantialities. The only difference that I can see between a theologian and a metaphysician is that, whereas the former personifies a generality which is the creation of his imagination, calling it a god, the latter objectifies a particularity which is the creation of his imagination calling it an entity; but all such personifications and objectifications (gods, things-in-themselves, vital entities, souls) are alike fictitious, because the childish theologians and metaphysicians proceed on the basis of philosophically assumed realities, not on scientifically established facts which pave the way on which an adult proceeds. Comte analyzes the difference between the intellectuality of theological children, metaphysical youths and scientific adults as follows: In the theological state, the human mind, seeking the essential nature of beings, the first and final causes (the origin and purpose) of all effects--in short, absolute knowledge--supposes all phenomena to be produced by the immediate action of supernatural beings. In the metaphysical state, which is only a modification of the first, the mind supposes, instead of supernatural beings, abstract forces, veritable entities (that is, personified abstractions) inherent in all beings, and capable of producing all phenomena. What is called the explanation of phenomena is, in this stage, a mere reference of each to its proper entity.