correspondingly consummate end;[224] while, again, in dealing with those precursors of Mr. Darwin, if such they can be called, who argued that the utility of an organ does not disprove its spontaneous origin, since only the creatures which, by a happy accident, came to possess it would survive—he answers that the constant reproduction of such organs is enough to vindicate them from being the work of chance;[225] thus displaying his inability to distinguish between the two ideas of uniform causation and design. As a result of the foregoing criticism, Aristotle distinguishes four different causes or principles by which all things are determined to be what they are—Matter, Form, Agent, and Purpose.[226] If, for example, we take a saw, the matter is steel; the form, a toothed blade; the agent or cause of its assuming that shape, a smith; the purpose, to divide wood or stone. When we have enumerated these four principles, we have told everything that can be known about a saw. But Aristotle could not keep the last three separate; he gradually extended the definition of form until it absorbed, or became identified with, agent and purpose.[227] It was what we should call the idea of function that facilitated the transition. If the very essence or nature of a saw implies use, activity, movement, how can we define it without telling its purpose? The toothed blade is only intelligible as a cutting, dividing instrument. Again, how came the saw into being? What shaped the steel into that particular form? We have said that it was the smith. But surely that is too vague. The smith is a man, and may be able to exercise other trades as well. Suppose him to be a musician, did he make the saw in that capacity? No; and here comes in a distinction which plays an immense part in Aristotle’s metaphysics, whence it has passed into our every-day speech. He does not make the saw _quâ_ musician but _quâ_ smith. He can, however, in the exercise of his trade as smith make many other tools—knives, axes, and so forth. Nevertheless, had he only learned to make saws it would be enough. Therefore, he does not make the saw _quâ_ axe-maker, he makes it _quâ_ saw-maker. Nor, again, does he make it with his whole mind and body, but only with just those thoughts and movements required to give the steel that particular shape. Now, what are these thoughts but the idea of a saw present in his mind and passing through his eyes and hands, till it fixes itself on the steel? The immaterial form of a saw creates the real saw which we use. Let us apply the preceding analogies to a natural object; for example, a man. What is the Form, the definition of a man? Not a being possessing a certain outward shape, for then a marble statue would be a man, which it is not; nor yet a certain assemblage of organs, for then a corpse would be a man, which, according to Aristotle, criticising Democritus, it is not; but a living, feeling, and reasoning being, the end of whose existence is