Bergson has pointed out that man might well be called _Homo Faber_. He is distinguished as the tool-making animal. This has held good since man was man; but till nature was construed in mechanical terms, the making of tools with which to attack and transform nature was sporadic and accidental. Under such circumstances it would not have occurred even to a Bergson that man's tool-making capacity was so important and fundamental that it could be used to define him. The very things that make the nature of the mechanical-physical scientist esthetically blank and dull are the things which render nature amenable to human control. When qualities were subordinated to quantitative and mathematical relationships, color, music and form disappeared from the object of the scientist's inquiry as such. But the remaining properties of weight, extension, numerable velocity of movement and so on were just the qualities which lent themselves to the substitution of one thing for another, to the conversion of one form of energy into another; to the effecting of transformations. When chemical fertilizers can be used in place of animal manures, when improved grain and cattle can be purposefully bred from inferior animals and grasses, when mechanical energy can be converted into heat and electricity into mechanical energy, man gains power to manipulate nature. Most of all he gains power to frame _new_ ends and aims and to proceed in regular system to their actualization. Only indefinite substitution and convertibility regardless of quality render nature manageable. The mechanization of nature is the condition of a practical and progressive idealism in action.