But further than this, in this conception of system the operation of the notion is not exhausted in the _existent unity_ of independent bodies as essential parts of it. For just as the differences are real the unity which relates them to the totality has to assert itself as real. This unity, in other words, differentiates itself from the multifold particularity of those objective bodies of which it is the integrating principle. And on this plane of existence it is differentiated therefore itself against such a particularity as real, independent and objective existence. In the solar system the sun exists over against all particularity related to that system, as such a unity of the system. Such a material existence of the ideal unity of the notion is still very defective; for whereas on the one hand we have this unity posited in its reality only as the relation or material connection between the severally independent bodies, on the other we have it posited as a body which belongs to that system, whose unity, in opposition to its real differences, it essentially represents. The sun, in short, which we take to be[202] the soul of the system, has itself an independent entity apart from the members which form the explicit content of this soul. It is itself only _one_ particular mode or phase of the notion, that, namely, of unity in its _difference_ from the actual separation of the several parts, a unity which remains outside itself, and is consequently abstract. For however much the sun by virtue of its physical quality is plainly a principle of unity, the illuminating body as such, this is after all merely an abstract identity. For light is simple, undifferentiated appearance and nothing more. We find therefore in the solar system the unity of the notion indeed objective, and the totality of its differences explicitly realized, each body making visible _one_ particular phase[203] of the notion; but here, too, it lies absorbed in its objective reality, and it fails to assert itself in such material as is truly inherent and explicit ideality. The form of its existence which here prevails remains the independent segregation of its particular phasal units[204].