The root of thought in all these men is the idea of development, the great formative idea of the present century. This idea however had an English as well as a German growth. In England it is best known through Darwin. But while Darwin shows its scientific side, the most celebrated of recent English philosophers, Mr. Herbert Spencer (1820), makes it the basis of a philosophy. _The Synthetic Philosophy_, just completed, is distinguished for the vastness of its design, the accomplishment of which gives Mr. Spencer a place among the few encyclopædic thinkers of the world. His philosophy is interesting also because it concentrates and reflects the spirit of the time. No other thinker has so strenuously laboured to gather together all the accumulations of modern knowledge and _to_ unite them under general conceptions. The alliance between the Spencerian philosophy and physical science is unusually close; and Mr. Spencer in his illustrations shows an all-embracing range of knowledge, which becomes minute in those branches of science bearing directly upon the phenomena of life. The future only can determine the exact value of this knowledge, for there are grave differences of opinion between Mr. Spencer and some of the leading biologists, like Weismann; but it may at least be said of him that he is the first philosopher since Bacon ('who wrote on science like a Lord Chancellor'), or at latest Leibnitz, who has met men of science on something like equal terms within the domain of science. Mr. Spencer's unique interest is that he has attempted an exhaustive survey of all the facts relating to the development of life and of society. He does not go beyond that, to the origin of all things; for it is one of his cardinal principles that behind the Knowable there is dimly visible a something not only unknown but unknowable. We are compelled to regard every phenomenon as the manifestation of an infinite and incomprehensible Power. In this the philosopher finds the reconciliation of religion with science; a reconciliation for which the religious have seldom shown much gratitude, because they are forbidden to say anything specific about the Power whose existence they may, and indeed must, assume. On this point there is a quarrel between Mr. Spencer and the metaphysicians, who dispute the right of any man to assert the existence of an Unknowable. If we can assert its existence surely we know it at least in part; and if so may we not by investigation come to know it better?