_Realism_ necessarily leads, as we have said, to _materialism_. For if empirical perception gives us things in themselves, as they exist independently of our knowledge, experience also gives us the _order_ of things in themselves, _i.e._, the true and sole order of the world. But this path leads to the assumption that there is only _one_ thing in itself, matter; of which all other things are modifications; for the course of nature is here the absolute and only order of the world. To escape from these consequences, while realism remained in undisputed acceptance, spiritualism was set up, that is, the assumption of a second substance outside of and along with matter, an _immaterial substance_. This dualism and spiritualism, equally unsupported by experience and destitute of proof and comprehensibility, was denied by Spinoza, and was proved to be false by Kant, who dared to do so because at the same time he established idealism in its rights. For with realism materialism, as the counterpoise of which spiritualism had been devised, falls to the ground of its own accord, because then matter and the course of nature become mere phenomena, which are conditioned by the intellect, as they have their existence only in its _idea_. Accordingly spiritualism is the delusive and false safeguard against materialism, while the real and true safeguard is idealism, which, by making the objective world dependent upon us, gives the needed counterpoise to the position of dependence upon the objective world, in which we are placed by the course of nature. The world from which I part at death is, in another aspect, only my idea. The centre of gravity of existence falls back into the _subject_. What is proved is not, as in spiritualism, that the knower is independent of matter, but that all matter is dependent on him. Certainly this is not so easy to comprehend or so convenient to handle as spiritualism, with its two substances; but χαλεπα τα καλα.