(1) The first moment or preparatory stage, does not belong to our subject. It requires, however, a word in passing. In all science, whether well or ill established, firm or weak, we start from facts derived from observation or experiment. Here, facts are replaced by general ideas. The terminus of every science is, then, the starting-point of philosophical speculation:—metaphysics begins where each separate science ends; and the limits of the latter are theories, hypotheses. These hypotheses become working material for metaphysics which, consequently, is an hypothesis built on hypotheses, a conjecture grafted on conjecture, a work of imagination superimposed on works of imagination. Its principal source, then, is imagination, to which reflection applies itself.

Metaphysicians, indeed, hold that the object of their researches, far from being symbolic and abstract, as in science, or fictitious and imaginary, as in art, is the very essence of things,—absolute reality. Unfortunately, they have never proven that it suffices to seek in order to find, and to wish in order to get.

(2) The second stage is critical. It is concerned with finding the principle that rules and explains everything. In the invention of his theory the metaphysician gives his measure, and permits us to value his imaginative power. But the hypothesis, which in science is always provisional and revocable, is here the supreme reality, the fixed position, the inconcussum quid.

The choice of the principle depends on several causes: The chief of these is the creator's individuality. Every metaphysician has a point of view, a personal way of contemplating and interpreting the totality of things, a belief that tends to recruit adherents.

Secondary causes are: the influence of earlier systems, the sum of acquired knowledge, the social milieu, the variable predominance of religions, sciences, morality, esthetic culture.

Without troubling ourselves with classifications, otherwise very numerous, into which we may group systems (idealism, materialism, monism, etc.) we shall, for our purpose, divide metaphysicians into the imaginative and rational, according as the imagination is superior to the reason or the reason rules the imagination. The differences between these two types of mind, already clearly shown in the choice of the hypothesis, are proven in its development.

(3) The fundamental principle, indeed, must come out of its state of involution and justify its universal validity by explaining everything. This is the third moment, when the scientific process of verification is replaced by a process of construction.

All imaginative metaphysics have a dynamic basis, e.g., the Platonic Ideas, Leibniz' Monadology, the Nature-philosophy of Schelling, Schopenhauer's Will, and Hartmann's Unconscious, the mystics, the systems that assume a world-soul, etc. Semi-abstract, semi-poetic constructions, they are permeated with imagination not only in the general conception, but also in the numberless details of its application. Such are the "fulgurations" of Leibniz, those very rich digressions of Schopenhauer, etc. They have the fascination of a work of art as much as that of science, and this is no longer questioned by metaphysicians themselves;[118] they are living things.

Rational metaphysics, on the other hand, have a chilly aspect, which brings them nearer the abstract sciences. Such are most of the mechanical conceptions, the Hegelian Dialectic, Spinoza's construction more geometrico, the Summa of the Middle Ages. These are buildings of concepts solidly cemented together with logical relations. But art is not wholly absent; it is seen in the systematic concatenation, in the beautiful ordering, in the symmetry of division, in the skill with which the generative principle is constantly brought in, in showing it ever-present, explaining everything. It has been possible to compare these systems with the architecture of the Gothic cathedrals, in which the dominant idea is incessantly repeated in the numberless details of the construction, and in the branching multiplicity of ornamentation.

Further, whatever view we adopt as to its ultimate value, it must be recognized that the imagination of the great metaphysicians, by the originality and fearlessness of its conceptions, by its skill in perfecting all parts of its work, is inferior to no other form. It is equal to the highest, if it does not indeed surpass them.