There are many persons no doubt who regard utility, not as a primary stage, but as the final and highest result of science. But the highest achievements of science, even the highest practical achievements, would never have been reached by the mere utilitarian. There is a force within us by which we are moved in the direction of acquiring knowledge for its own sake and for the sake of truth, regardless of any material advantage to be derived from such knowledge. Sooner or later such knowledge is sure to bear practical fruits, even though we may not live to realize them.
It is in this spirit that men of science have advanced to the second or classificatory stage, in which, with a view to higher generalization, the subjects studied are grouped together according to their affinities, and specific points of resemblance are taken as the representatives of each class.
These classes are at first grouped round independent centres; but such an arrangement of them, having no existence in reality, is purely subjective and can only be transitional. The margins of the classes so formed represent only the margins of our knowledge or our ignorance, as the case may be.
By degrees, as the classes become extended, sub-classes are formed, and they are seen to arrange themselves in the form of branches radiating from a central stem. By still further observation, the stems of the several classes are seen to tend towards each other, and we are led to trace them to a point of union.
Thus from the classificatory or comparative we pass gradually into the third stage, which I have spoken of as the theoretical, but which may perhaps be more clearly defined as the evolutionary. By the use of this term ‘evolutionary’ we make it apparent that our third stage is but a development of the second, evolution being merely the necessary and inevitable result of the extension of classification, implying greater unity and broader generalizations.
These three stages then, the empirical or practical, the classificatory or comparative, and the evolutionary, are applicable to the development of all the inductive sciences.
But it has been held by some that a broad line of demarcation must be drawn between the physical sciences properly so called, such as zoology, botany, and geology, which deal with external nature, and those sciences which have been termed historic, which deal with the works of man.