The comments of a number of mechanistic biologists on vitalism furnish the point of departure for Dewey's discussion. These scientists hold that, if the organism is considered simply as a part of external nature, as an existing system, it can be satisfactorily analyzed by the methods of physico-chemical science. But if the question of ultimate origins is raised, if it be asked _why_ nature exhibits certain innate potentialities for producing life, science can give no answer. These questions belong to metaphysics, and vitalistic or biocentric conceptions may be valid in the metaphysical sphere. This raises the question of the nature of metaphysical inquiry. Dewey says that the ultimate traits or tendencies which give rise to life need not necessarily be considered ultimate in a temporal sense. On the contrary, they may be viewed as permanent, 'irreducible traits,' which are ultimate in the sense of being always present in reality. The inquiry and search for these ultimate traits is what constitutes valid metaphysics. "They are found equally and indifferently whether a subject-matter in question be dated 1915 or ten million years B. C. Accordingly, they would seem to deserve the name of ultimate, or irreducible, traits. As such they may be made the object of a kind of inquiry differing from that which deals with the genesis of a particular group of existences, a kind of inquiry to which the name metaphysical may be given."[272] The irreducible traits which Dewey finds are, in the physical sciences, plurality, interaction, and change. "These traits have to be begged or taken in any case," for wherever and whenever we take the world, we must explain it as "a plurality of diverse interacting and changing existences."[273] The evolutionary sciences add another trait; that is, evolution, or development in a direction. "For evolution appears to be just one of the irreducible traits. In other words, it is a fact to be reckoned with in considering the traits of diversity, interaction, and change which have been enumerated as among the traits taken for granted in all scientific subject-matter."[274]