The unity of the universe does not consist in its existence, although its existence is a presumption of its unity, since it must first exist before it can be a unit. Existence beyond the boundary line of our horizon is an open question. The real unity of the universe consists in its materiality, and this is established, not by a pair of juggling phrases but by means of a long and difficult development of philosophy and natural science. With respect to the subject in hand; the existence which Herr Duehring presents to us is "not that pure existence which is self sufficient and without any other qualities, in fact, only representing the antithesis of no-idea or absence-of-idea." Now we shall very soon see that the universe of Herr Duehring has its origin simultaneously with an existence which is without essential differentiation, progress or change, and is therefore merely in fact a contradiction of absence of thought, therefore really nothing. From this non-existence is developed the present differentiated, changeable universe which represents progressive growth; and when we grasp this idea, only by virtue of this eternal change do we arrive at "the concept of the self sufficing, universal existence." We have therefore now the concept of existence on a higher plane where it comprises within itself stability as well as change, being as well as development. Arrived at this point we find that "species and genera in fact the special and the general, are the simplest forms of differentiation, without which the constitution of things cannot be grasped." But this is a means of distinguishing quality and after a discussion of this part of the subject we proceed "Over against the idea of species stands the idea of the whole, a homogeneity, as it were, in which no differentiation of species can longer be found," so we pass from quality to quantity and this is always "capable of measurement."