This third position isarelic of ancient metaphysical realism; although it must be remembered that Kant does not go to the length of Descartes and Locke, who supposed that from mere ideas we could know bodies and souls, but suggests that beneath the phenomena of outer and inner sense the thing in itself may not be heterogeneous (ungleichartig).
As long as even the meagre realism of the Kantian thing in itself is maintained, the account of there being one sun is simply that one thing causes different phenomena in different minds.
He maintained that the physical and the psychical are two orders which are parallel without interference; that the physical or objective order is merely phenomena, or groups of feelings, or " objects," while the psychical or subjective order is both a stream of feelings of which we are conscious in ourselves, and similar streams which we infer beyond ourselves, or, as he came to call them, " ejects "; that, if we accept the doctrine of evolution at all, we must carry these ejective streams of feelings through the whole organic world and beyond it to the inorganic world, as a " quasimental fact "; that at bottom both orders, the physical phenomena and the psychical streams, are reducible to feelings; and that therefore there is no reason against supposing that they are made out of the same " mind-stuff," which is the thing-in-itself.
Admitting Kant's hypothesis that by inner sense we are conscious of mental states only, he holds that this consciousness constitutes a knowledge of the "thing-in-itself" - which Kant denies.
Since form cannot produce matter nor subject object, we are forced to assume a thing-in-itself.
