In this way, however, the revolutionary side of Hegelian philosophy was again taken up and at the same time freed from the idealist trimmings which with Hegel had prevented its consistent execution. The great basic thought that the world is not to be comprehended as a complex of readymade things, but as a complex of processes, in which the things apparently stable no less than their mind images in our heads, the concepts, go through an uninterrupted change of coming into being and passing away, in which, in spite of all seeming accidentally and of all temporary retrogression, a progressive development asserts itself in the end -- this great fundamental thought has, especially since the time of Hegel, so thoroughly permeated ordinary consciousness that in this generality it is now scarcely ever contradicted. But to acknowledge this fundamental thought in words and to apply it in reality in detail to each domain of investigation are two different things. If, however, investigation always proceeds from this standpoint, the demand for final solutions and eternal truths ceases once for all; one is always conscious of the necessary limitation of all acquired knowledge, of the fact that it is conditioned by the circumstances in which it was acquired. On the other hand, one no longer permits oneself to be imposed upon by the antithesis, insuperable for the still common old metaphysics, between true and false, good and bad, identical and different, necessary and accidental. One knows that these antitheses have only a relative validity; that that which is recognized now as true has also its latent false side which will later manifest itself, just as that which is now regarded as false has also its true side by virtue of which it could previously be regarded as true. One knows that what is maintained to be necessary is composed of sheer accidents and that the so-called accidental is the form behind which necessity hides itself -- and so on.
The old method of investigation and thought which Hegel calls "metaphysical", which preferred to investigate things as given, as fixed and stable, a method the relics of which still strongly haunt people's minds, had a great deal of historical justification in its day.
It was necessary first to examine things before it was possible to examine processes. One had first to know what a particular thing was before one could observe the changes it was undergoing. And such was the case with natural science. The old metaphysics, which accepted things as finished objects, arose from a natural science which investigated dead and living things as finished objects. But when this investigation had progressed so far that it became possible to take the decisive step forward, that is, to pass on the systematic investigation of the changes which these things undergo in nature itself, then the last hour of the old metaphysic struck in the realm of philosophy also. And in fact, while natural science up to the end of the last century was predominantly a collecting science, a science of finished things, in our century it is essentially a systematizing science, a science of the processes, of the origin and development of these things and of the interconnection which binds all these natural processes into one great whole. Physiology, which investigates the processes occurring in plant and animal organisms; embryology, which deals with the development of individual organisms from germs to maturity; geology, which investigates the gradual formation of the Earth's surface -- all these are the offspring of our century.
But, above all, there are three great discoveries which have enabled our knowledge of the interconnection of natural processes to advance by leaps and bounds: first, the discovery of the cell as the unit from whose multiplication and differentiation the whole plant and animal body develops. Not only is the development and growth of all higher organisms recognized to proceed according to a single general law, but the capacity of the cell to change indicates the way by which organisms can change their species and thus go through a more than individual development.
Second, the transformation of energy, which has demonstrated to us that all the so-called forces operative in the first instance in inorganic nature -- mechanical force and its complement, so-called potential energy, heat, radiation (light, or radiant heat), electricity, magnetism, and chemical energy -- are different forms of manifestation of universal motion, which pass into one another in definite proportions so that in place of a certain quantity of the one which disappears, a certain quantity of another makes its appearance and thus the whole motion of nature is reduced to this incessant process of transformation from one form into another.
Finally, the proof which Darwin first developed in connected form that the stock of organic products of nature environing us today, including man, is the result of a long process of evolution from a few originally unicellular germs, and that these again have arisen from protoplasm or albumen, which came into existence by chemical means.
