According to the view of science, concepts have their origin in experience and come to be through the discarding, the letting drop, of the unessential. But in order that a concept may come into existence after such a fashion, it is necessary that it exist beforehand as a thing given, in the same way that a statue can only come forth from out the block of marble through the discarding of the unessential, when it is already given ideally in the mind of the artist.[36] As already remarked, all attempts to frame a view of the world upon purely scientific lines, to comprehend the play of world-events as simple relation-values, present themselves in a twofold form. Making physics its point of departure and from thence working its way forward, one view endeavours to prove the law of the conservation of energy valid also for non-reversible processes; this is the world-theory of energetics. The other view follows the results of criticism; this is modern positivism. The entire value of the world-theory of energetics is distinguished by the following consideration:-- Its axis, its thorough bass--so to speak--is the law of the conservation of energy; once this gives way, no energical world-theory is possible. As, however, has been explained in another place, nowhere in actuality do conditions obtain corresponding to this law. Its existence merely as a possibility demands an artificial premiss--a completely closed system; but this exists only as an ideal ultimate concept (_Grenzbegriff_)--nowhere in actuality. If it is desired to make use of the law of the conservation of energy with a view to erecting a world-theory thereupon, one must set up the entire universe hypothetically as a closed system in itself. The logical consequences that necessarily follow from this supposition are detailed at the close of Essay VI. The purely ideal nature of the point of view occupied by science in this whole picture of the world is at once evident from the simple fact that, in order to maintain the constancy of the sum of energy in the universe, she here finds herself in the predicament of still having to “handle” as energy heat that no longer permits of being transformed into mechanical work--that is, heat that exists only as an empty concept. At this stage I wish once more to insist that this entire world-theory does not at all operate with actual energies, but only with the _expression_ of actual energies, with their _reaction_ as presented in _work done_. It assumes work and energy to be synonymous; which is about the same as if one assumed shadow and light to be synonymous. As shadow attests nothing save that light is present, but attests this of necessity, so work attests nothing save that energy is present. Ostwald in his _Naturphilosophie_, after expressly assuming work and energy to be alike, proceeds thus:--