This unity, which embraces all the knowable, is the subject of the fifth dialogue of the _Causa_. The steps by which we have reached it are:--first, the identification of a common nature, or _substratum_ in things corporeal,--corporeal matter, that which is common to all physical existences; secondly, the recognition that there must similarly be a corresponding matter, or common ground of things spiritual; there also differences exist and demand an identity; and finally, corporeal matter and spiritual matter must themselves coincide in ground; there must exist that which is indifferently either, or which is the potency of both, and their "subject" or substratum. To the objection that to have dimensions is characteristic of matter, it is answered that each kind of matter _has_ dimensions, only the latter has them absolutely, _i.e._ it has all indifferently, and therefore none, while the other is always "contracted" to one or other at each instant, but has all successively. We have seen that at the close of the fourth dialogue Bruno refers again to the first principle, unknowable, or knowable only by faith, and professes to abstain from any consideration of it. It is quite clear, however, that Bruno could not have said of it anything other than he says of this unity of the corporeal and the spiritual itself. That which is implicitly all reality in such a manner that it is at the same time none of the particular forms of the real, is all things and none--could not be other than the highest principle. Further, this unity already has the distinction applied formerly to the Highest Intelligence,--it "is all," and at the same time it "creates all," in producing the forms out of itself. The unity then is only the world-soul from a special point of view, or the world-soul is at once the unity of itself and of the corporeal world.[280] This means that of the spiritual and the corporeal worlds each is a unity in itself, and each only a special aspect of a final unity which embraces both. It is no wonder then that Schelling found a congenial spirit in Bruno. The reality of this final matter or unity is moreover higher, truer, than that of any of the forms to which it gives birth, and finally it is _divine_. Little more is wanting to prove the entire superfluity of the theological highest principle. The unity (or matter) is by no means an "abstract" identity, but a concrete whole, which contains all differentiation in itself, and a "dynamic" being, which produces, or realises, its own modes. "Determinate, sensible, _explicate_ existence is not the highest characteristic (_raggione_) of actuality, but is a thing consequent, an effect of the latter; thus the principal essence of wood, _e.g._ the characteristic of its actuality, does not consist in its being 'bed'; but in its being of such a substance and consistency that it _may be_ bed, bench, beam, idol, or anything formed of wood. Nature, however, from its material produces all things, not