The doctrine that evolution consists in nothing but movements in space, amounts to the assertion that we know nothing about things and men except that they move. In point of fact, we know a good deal more. We know that men think, and that the movement of thought is not a movement in space. We know that the vibrations of the ether are movements in space and that they are also something more: they are known to us also as sights, sounds, etc. No explanation or concise statement of the process of evolution can be satisfactory, or even scientific, which begins by denying the relevance and even the reality of the most important part of our knowledge. If the "first principles" of evolution are to be scientific, they must be inductions drawn from observation and based on some similarity in the phenomena observed, in which case, and in which case alone, they will apply to both classes of phenomena, mental and material. If any "principle" is true of one class alone, it is shown thereby not to be a "first principle": it is not universally applicable. This raises the question whether there can be any first principles in this sense, whether mind and matter are, to some extent, subject to the same laws; or whether the resemblances which are sometimes drawn are not merely metaphors more or less expanded. Thus we speak of "weighty" objections; but will anyone maintain that ideas are subject to, or exemplify, the law of gravitation? We speak of ideas as "coherent" or "incoherent"; does anyone suppose that they stick together in the same way and from the same causes as material objects cohere? Mr. Herbert Spencer has written a chapter[21] under the title "Society is an Organism," in which he points out many resemblances between society and an organism. But Mr. Spencer himself "distinctly asserts"[22] that the resemblances imply nothing more than that in both society and organisms there is "a mutual dependence of parts." That is to say, sociology does not herein "exemplify" some of the laws of biology, but sociology and biology both exemplify certain laws which hold good wherever there is a mutual dependence of parts.