It appears to us that, if a philosophy is to assume this rôle and to undertake the guidance of man's thought and action, it must bring forward general principles of such breadth that they will apply to all orders of phenomena, from the simplest to the most complex—a system of laws coördinated by deductive relations, and by its universality expressing all the phenomena of the universe. Whether these general principles are given a priori, as the intuitionists hold, or whether they are the abstract expression of an experience invariably and unconditionally repeated, at all events they must be such that from them all our scientific theories may be deduced; they must appear in all our researches as the criterion of the truth of the results, and they must underlie all our anticipations of truth as the guiding principles. Causes, that is to say, the sum of the antecedent phenomena, whose joint action is necessary for the production of the consequent phenomenon, or effect, may be as diverse as you please, nevertheless their relation to their effect will be expressed by the same general law.
A philosophy of biology must reduce under these principles of philosophy all the truths furnished by experience in the various branches of investigation pertaining to that science; must explain them by these principles; must present them to us as necessary, and the contrary results as illogical and unphilosophical, so as to produce a twofold effect, viz., the highest possible harmony in the system of our knowledges, and an ever-strengthening confirmation of the general principles which are their abstract expression. We must demand of it a verdict upon doctrines respecting the constitution of the living individual and its origin and the constitution of the species to which the individual belongs, which verdict shall oblige us to accept these doctrines as corollaries of the same general principles from which the accepted theories of the other abstract sciences are likewise deduced. Finally, we must derive from this philosophy of biology the assurance that the generalizations which it offers to us are grounds upon which we can stand securely in our deductions—of course within the province of biology—respecting man and the human species.
Mr. Herbert Spencer attempts something like this when he rests the laws of biology upon the theory of changes in the course of things, as set forth in his "First Principles." The "Principles of Biology" is the first application of his system of philosophy to a highly-complex order of phenomena.
It will be well to give a sketch of Mr. Spencer's whole system, so that we may better understand the meaning of the abstract terms he employs, and the relations between the general laws on which the system is based. We shall thus be in a position to appreciate the author's application of his system to the more restricted field of biology.
Underlying Spencer's system we find the principle of the persistence of force, "the sole truth which transcends experience," to which
