In the first book the world was shown to be mere representation, object for a subject. In the second book, we considered it from its other side, and found that this is will, which proved to be simply what this world is besides being representation. In accordance with this knowledge, we called the world as representation, both as a whole and in its parts, the objectivity of the will, which accordingly means the will become object, i.e., representation. Now we recall further that such objectification of the will had many but definite grades, at which, with gradually increasing distinctness and completeness, the inner nature of the will appeared in the representation, in other words, presented itself as object. In these grades we recognized the Platonic Ideas once more, namely in so far as such grades are just the definite species, or the original unchanging forms and properties of all natural bodies, whether organic or inorganic, as well as the universal forces that reveal themselves according to natural laws. Therefore these Ideas as a whole present themselves in innumerable individuals and in isolated details, and are related to them as the archetype is to its copies. The plurality of such individuals can be conceived only through time and space, their arising and passing away through causality. In all these forms we recognize only the different aspects of the principle of sufficient reason that is the ultimate principle of all finiteness, of all individuation, and the universal form of the representation as it comes to the knowledge of the individual as such. On the other hand, the Idea does not enter into that principle; hence neither plurality nor change belongs to it. While the individuals in which it expresses itself are innumerable and are incessantly coming into existence and passing away, it remains unchanged as one and the same, and the principle of sufficient reason has no meaning for it. But now, as this principle is the form under which all knowledge of the subject comes, in so far as the subject knows as an individual, the Ideas will also lie quite outside the sphere of its knowledge as such. Therefore, if the Ideas are to become object of knowledge, this can happen only by abolishing individuality in the knowing subject. The more definite and detailed explanation of this is what will now first concern us.