In my opinion [he writes] the three transcendental problems (1, 2 and 5) are settled by our conception of substance; the three which he [Du Bois-Reymond] considers difficult, though soluble[47] (3, 4 and 6) are decisively answered by our modern theory of evolution; the seventh and last, the freedom of the will, is not an object for critical scientific inquiry at all, for it is a pure dogma, based on an illusion, and has no real existence. How far such a mode of rebuking dogmatism appears convincing, must of course depend on what the reader understands by an argument. Some points already considered may help us to a right estimate of proofs which are based upon "Our conception of substance," or "Our modern theory of evolution," and we shall presently inspect more closely the nature of the difficulties which we are invited so summarily to dismiss. Meanwhile, even though not final or conclusive, the testimony of such a man as Du Bois-Reymond serves at least to prove that it is possible to be thoroughly familiar with Science and her teaching, and yet to believe that as yet she knows nothing at all concerning questions which, as we have been assured, she has conclusively answered. And, as we shall presently see, if Professor Haeckel's account of things be the true one, there are many more scientific men of the first rank who are equally in the dark. In a word, while according to Professor Haeckel there is in the universe but one Riddle, which he tells us he has solved,--in the opinion of another who is certainly no less entitled to speak in the name of Science, there yet remain seven to which no answer has yet been given, and to three, at least, of which none will ever be found. VIII MATTER AND MOTION In the forefront of the problems which have been pronounced to be not only unsolved but insoluble, are the nature and origin of the ultimate factors arrived at by Science in her study of the constitution of the universe,--Matter, Force, and Motion. With the first and last of these alone need we at present concern ourselves, for "Force," as Science knows it, is always associated with Matter, and signifies no more in her terminology than that which produces, or tends to produce Motion. On the other hand, we are told,[48] that "The contents of the material universe may be expressed in terms of Matter and Motion." By "Matter" is understood "Sensible Substance," the stuff composing all of which our senses tell us, and which forms the object of Scientific investigation. What do we know concerning this raw material whereof worlds are made?