The nature of scientific "explanation" is well understood by men of science (in England, at least), and has been made familiar to the non-scientific world by John Stuart Mill. An event is scientifically "explained" when it is shown to be a case of a general law; a law is "explained" when it is shown to come under some more general law. In other words, the business of science is to show that the thing under examination always happens (or tends to happen) under certain circumstances which science can formulate with more or less exactness. But _how_ or _why_ the thing should happen thus, science does not undertake to explain: "what is called explaining one law of nature by another, is but substituting one mystery for another; and does nothing to render the general course of nature other than mysterious: we can no more assign a _why_ for the more extensive laws than for the partial ones."[9] It is only "minds not habituated to accurate thinking" which imagine that the laws are the _causes_ of the events which happen in accordance with them, "that the law of general gravitation, for example, causes the fall of bodies to the earth."[10] It may be a law of science, a perfectly true statement, that the phenomenon B always follows the phenomenon A; but that statement, true as it is, is not the cause of B. _That_ A is always followed by B is demonstrated by science. _Why_ it should be followed by B is as mysterious as magic--as mysterious as that the waving of the magician's wand should be immediately followed by the rising of a palace from the ground. How the one thing _can_ follow the other, is no part of science's business to explain. Science, therefore, is essentially descriptive: with ever-increasing accuracy it describes things and the order in which they happen. Evolution, then, as a scientific theory, is also purely descriptive: it describes the way in which things have come to be what we see them to be, the process by which the totality of things has come to be what it is. But when the purely scientific and descriptive part of the work is done, when science has formulated the order of the events which have led up to the existing state of the universe, when the process of evolution has been described, there still remain the questions which science refused even to try to answer, and there also remain other questions more vital to science. There arises the question, In what sense is evolution a real process? do the laws of science exist only in the minds of men of science? is the process of evolution merely the description which is given of it (as according to some thinkers a thing is only the sensations which we have of it), or is it something more?