4. Thus far the one school. But while this Theoretic Conception stripped Nature of consciousness, motive, and passion, rendering it a mere aggregate of mathematical relations, a critical process was going on, which, analyzing the nature of Perception, was rapidly moving towards another goal. Locke, Berkeley, Hume, and Kant, directing their analysis exclusively to the subjective aspect of phenomena, soon broke down the barriers between the physical and mental, and gradually merged the former in the latter. Matter and its qualities, hitherto accepted as independent realities, existing where no Mind perceived them, were now viewed as the creations of Mind--their existence was limited to a state of the percipient. The old Dualism was replaced by Idealism. The Cosmos, instead of presenting a problem of Mechanics, now presented a problem of Psychology. Beginning with what are called the secondary qualities of Matter, the psychological analysis resolved these into modes of Feeling. “The heat which the vulgar imagine to be in the fire and the color they imagine in the rose are not there at all, but are in us--mere states of our organism.” Having gained this standing-place, there was no difficulty in extending the view from the secondary to the primary qualities. These also were perceptions, and only existed in the percipient. Nothing then remained of Matter save the hypothetical unknown _x_--the postulate of speculation. Kant seemed forever to have closed the door against the real Cosmos when he transformed it into a group of mental forms--Time, Space, Causality, Quantity, etc. He propounded what may be called a theory of mental Dioptrics whereby a pictured universe became possible, as Experience by its own _a priori_ laws moulded _itself_ into a consistent group of appearances, which produced the illusion of being a group of realities. He admitted, indeed, that by the operation of Causality we are compelled to believe in a Real underlying the appearances; but the very fact that this Causality is a _subjective law_, is proof, he said, of its not being an _objective truth_. Thus the aim of the mechanical conception was to free research from the misleading complexities of subjective adulterations, and view _things as they are_ apart from their _appearances_; but this aim seemed illusory when Psychology showed that Time, Space, Matter, and Motion were themselves not objective reals except in so far as they represented subjective necessities; and that, in short, things _are_ just what they _appear_, since it is only in the relation of external reals to internal feelings that objects exist for us.