The problem of the nature of life, of the principle of vitality, is almost as old as philosophy itself, and from the earliest times in which men began to ponder over the problem, the same antitheses have been apparent which we find to-day. Disguised under various catchwords and with the greatest diversities of expression, the antitheses remain essentially the same through the centuries, competing with one another, often mingling curiously, so that from time to time one or other almost disappears, but always crops up again, so that it seems as if the conflict would be a never-ending one—the antitheses between the mechanical and the “vitalistic” view of life. On the one side there is the conviction that the processes of life may be interpreted in terms of natural processes of a simple and obvious kind, indeed directly in terms of those which are most general and most intelligible—namely, the simplest movements of the smallest particles of matter, which are governed by the same laws as movement in general. And associated with this is the attempt to take away any special halo from around the processes of life, to admit even here no other processes but the mechanical ones, and to explain everything as the effect of material causes. On the opposite side is the conviction that vital phenomena occupy a special and peculiar sphere in the world of natural phenomena, a higher platform; that they cannot be explained by merely physical or chemical or mechanical factors, and that, if “explaining” means reducing to terms of such factors, they do in truth include something inexplicable. These opposing conceptions of the living and the organic have been contrasted with one another, in most precise form and exact expression, by Kant in certain chapters of the Kritik der Urteilskraft, which must be regarded as a classic for our subject.(56) But as far as their general tendency is concerned, they were already represented in the nature-philosophies of Democritus on the one hand, and of Aristotle on the other.
All the essential constituents of the modern mechanical theories are really to be found in Democritus, the causal interpretation, the denial of any operative purposes or formative principles, the admission and assertion of quantitative explanations alone, the denial of qualities, the reduction of all cosmic developments to the “mechanics of the atom” (even to attractions and repulsions, thus setting aside the “energies”), the inevitable necessity of these mechanical sequences, indeed at bottom even the conviction of the “constancy of the sum of matter and energy.” (For, as he says, “nothing comes out of nothing.”) And although he makes the “soul” the principle of the phenomena of life, that is in no way contradictory to his general mechanical theory, but is quite congruent with it. For the “soul” is to him only an aggregation of thinner, smoother, and rounder atoms, which as such are more mobile, and can, as it were, quarter themselves in the body, but nevertheless stand in a purely mechanical relation to it.