The oscillation of the pendulum (including the rest at the close of each swing) is an example of the sort of fact requiring the distinction in question. If all energy is purely kinetic, then the constitution of matter is atomic in the merely mechanical sense, a notion now rejected by advanced physical speculation. Philosophically viewed, potential energy and kinetic energy are merely the necessary corresponding thetic and antithetic forms of the one concrete eternal energy constituting the substance of all real things; their notions flow from that of nature as eternal definite productivity.
As regards "evolution," natural science — i.e. the most highly generalized natural science — arranges phenomenal existences in ascending series consisting of groups differing by gradual variations, and affirms that the more indefinite, incoherent, and homogeneous forms are earlier than, and the parents of, the more definite, coherent, and heterogeneous, succeeding them. But natural science, since it knows only the given phenomena, does not, when it understands itself, pretend to have any conception of cause in any other sense than that of regular antecedent; all that it can mean by the assertion that the more definite, coherent, and heterogeneous forms are evolved from the more indefinite, incoherent, and homogeneous forms, is that they regularly follow them in the order of time. The philosophy of nature sees in an ascending series of gradually differing forms not merely a temporal succession, but the operation of a single energy in and for which the forms, though temporarily successive, are logically coexistent, the "later" being quite as much presupposed by the "earlier" as they presuppose the earlier, the two being "parts" of a whole, logically prior to either or both. The philosophical law of "evolution" in nature is that of an ascent in forms from indifferent or neutral indetermination through mere determination by others to self-determination, from mere abstract individuality to concrete individuality of being, in which latter the notion of the genus is all but realized in every individual, the whole is in every part. The terms of the scientific law of evolution are expressive of categories quite abstract, and of a comparatively low order even when taken in other than a purely
