It is fortunately unnecessary, here, to go further into details. What Herbart proposes is not a method for the mathematical measurement of psychic facts: it is a theory of mechanics and statics specially adapted to the peculiarities of psychical phenomena, where the forces are given with no sine or cosine, where instead of gravitation we have the constant effort (as it were elasticity) of each idea to revert to its unchecked state. He claims—in short—practically to be a Kepler and Newton of the mind, and in so doing to justify the vague professions of more than one writer on mind—above all, perhaps of David Hume, who goes beyond mere professions—to make mental science follow the example of physics. And a main argument in favour of his enterprise is the declaration of Kant that no body of knowledge can claim to be a science except in such proportion as it is mathematical. And the peculiarity of this enterprise is that self-consciousness, the Ego, is not allowed to interfere with the free play of psychic forces. The Ego is—psychologically—the result, the product, and the varying product of that play. The play of forces is no doubt a unity: but its unity lies not in the synthesis of consciousness, but in the essential unity of Soul. And Soul is in its essence neither consciousness, nor self-consciousness, nor mind: but something on the basis of whose unity these are built up and developed(33). The mere “representation” does not include the further supervenience of consciousness: it represents, but it is not as yet necessary that we should also be conscious that there is representation. It is, in the phrase of Leibniz, perception: but not apperception. It is mere straight-out, not as yet reflected, representation. Gradually there emerges through the operation of mechanical psychics a nucleus, a floating unity, a fixed or definite central aggregate.