Thus causal nature is a metaphysical chimera; though there is need of a metaphysics whose scope transcends the limitation to nature.

The object of such a metaphysical science is not to explain knowledge, but exhibit in its utmost completeness our concept of reality.
However, we must admit that the causality theory of nature has its strong suit.

The reason why the bifurcation of nature is always creeping back into scientific philosophy is the extreme difficulty of exhibiting the perceived redness and warmth of the fire in one system of relations with the agitated molecules of carbon and oxygen, with the radiant energy from them, and with the various functionings of the material body.

Unless we produce the all-embracing relations, we are faced with a bifurcated nature; namely, warmth and redness on one side, and molecules, electrons and ether on the other side.

Then the two factors are explained as being respectively the cause and the mind's reaction to the cause.
Time and space would appear to provide these all-embracing relations which the advocates of the philosophy of the unity of nature require.
The perceived redness of the fire and the warmth are definitely related in time and in space to the molecules of the fire and the molecules of the body.
It is hardly more than a pardonable exaggeration to say that the determination of the meaning of nature reduces itself principally to the discussion of the character of time and the character of space.