Mr. Herbert Spencer, the only English philosopher who has even attempted a _System_ of Philosophy, may in this point be compared with Hegel. He also begins with a _First Principles_,—a work which, like Hegel’s _Logic_, starts by presenting Philosophy as the supreme arbiter between the subordinate principles of Religion and Science, which are in it “necessary correlatives.” The positive task of philosophy is (with some inconsistency or vagueness) presented, in the next place, as a “unification of knowledge.” Such a unification has to make explicit the implicit unity of known reality: because “every thought involves a whole system of thoughts.” And such a programme might again suggest the Logic. But unfortunately Mr. Spencer does not (and he has Francis Bacon to justify him here) think it worth his while to toil up the weary, but necessary, mount of Purgatory which is known to us as Logic. With a naïve realism, he builds on Cause and Power, and above all on Force, that “Ultimate of Ultimates,” which seems to be, however marvellously, a denizen both of the Known and the Unknowable world. In the known world this Ultimate appears under two forms, matter and motion, and the problem of science and philosophy is to lay down in detail and in general the law of their continuous redistribution, of the segregation of motion from matter, and the inclusion of motion into matter. Of this process, which has no beginning and no end,—the rhythm of generation and corruption, attraction and repulsion, it may be said that it is properly not a first principle of all knowledge, but the general or fundamental portion of Natural Philosophy to which Mr. Spencer next proceeds. Such a philosophy, however, he gives only in part: viz. as a Biology, dealing with organic (and at a further stage and under other names, with supra-organic) life. And that the Philosophy of Nature should take this form, and carry both the First Principles and the later portions of the system with it, as parts of a philosophy of evolution, is what we should have expected from the contemporaneous interests of science(2). Even a one-sided attempt to give speculative unity to those researches, which get—for reasons the scientific specialist seldom asks—the title of biological, is however worth noting as a recognition of the necessity of a _Natur-philosophie_,—a speculative science of Nature.