Since the natural sciences cannot be unified in a concept (hence their ineradicable _plurality_), and therefore remain unsystematic, a mass of sciences without close relation among themselves, logical distinctions are not possible in any science. No one will ever be able to prove that genera and species must be so many and no more, or describe the truly original character by which one genus may be distinguished from another genus and one species from another species. The animal species hitherto described have been calculated it over four hundred thousand, and those that may yet be described as fifteen millions. These numbers simply express the impotence of the empirical sciences to exhaust the infinite and individual forms of the real and the necessity in which they are placed of stopping at some sort 1 of number, of some hundreds, of some thousands, or of some millions. Those species, however few or many they may be, flow one into the other owing to the undeniable conceivability of graduated, indeed of continuous intermediate forms, which made evident the arbitrariness of the clean cut made into fact by separating the wolf from the dog or the panther from the leopard. [Sidenote: _Laws in the natural sciences, and so called prevision._] But some doubt is manifested where we pass from classification and description or from _system_ (as the lack of system of naturalistic classifications is called, by a curious verbal paradox) to the consideration of the laws that are posited in those sciences. It is then perceived that the classification is certainly a simple labour of preparation, arbitrary, convenient, and nominalistic, but that the true end of the natural sciences is not the class but the _law._ In the compass of the law strict accuracy of its truth is indubitable; so much so that by means of laws it is actually possible to make _previsions_ as to what will happen. This is indeed a miraculous power, which places the natural sciences above every form of knowledge, and endows them with an almost magical force, by means of which man, not contented with knowing what has happened (which is yet so difficult to know), is capable of knowing even what has not yet happened, what will happen, or the future! _Prevision_(there must be a clear understanding of the concepts) is equivalent to _seeing beforehand or prophesying,_ and the naturalist is thus neither more nor less than a clairvoyant. [Sidenote: _Empirical character of naturalistic laws._]