There exists nothing but living minds of different degrees of energy. We men are small beings associated with a cosmical creature whose force is immeasurably greater than ours, and we have intelligence enough to utilise part of this force to supplement our own. That is the meaning of _mechanism_. Some efforts to control the cosmic forces are profitable, but there is no transmutation of our energy into the result, nor any necessary equivalence between the labour and the result. We may stumble upon an available cosmic force almost by accident--we may waste a life-time over a mechanical problem and fail to solve it. The utilisation of cosmic force by man is best explained by comparing it with animal slavery. Trap a wild elephant and train him to draw and carry--you have constructed an engine. There are of course important differences between the two kinds of instrument, due to the enormous disproportion between the magnitude and power of the respective entities. In the case of the animal the whole life comes under our control: in the case of the cosmos we can utilise only a minute fraction of it, and that rather by putting ourselves in its way than by making it obey us. The animal we have to feed: the cosmic being does not draw upon us for its nourishment. We can direct the animal through his sensibility: the cosmic sensibility appears to be beyond our power of irritation. Apart from these differences the general laws of the one kind of tool are those of the other also. We have not transferred power to the raised stone, or the coiled spring, or the loaded gun, or the embanked river--any more than to the tamed and harnessed horse. There is no fixed ratio between the fatigue of catching and training an animal, and the energy saved by making him work for us. The animal's work is not our own energy given back to us--neither is the machine's. A plough is useless without cattle to draw it--so is a turbine without water to drive it. When coal is burned to 'generate' electricity, that is the cosmic equivalent of exhausting or killing one animal to overpower or to feed another: the energy of combustion is utterly destroyed--not transformed into the electricity. The question can be more accurately stated and brought to a plain issue if we use the terms and forms of dialectic. A theory is an argument--when it is not a fallacy--and an argument, we have seen, consists of two parts. There is the matter of fact requiring explanation, and the antecedent knowledge which is used to illustrate it. Of these the precedent is the more important, and it is no valid objection to a criticism that the person who offers it knows less about the _case_ than the theorist. The critic may be in possession of a better precedent, which the theorist has failed to notice, perhaps from a too exclusive attention to the case.