6 UTILITARIAN SCIENCES 



causes and permits complexity in external relations. Safety in life 

 depends on choosing the right response to external stimulus. Wrong 

 choice leads to failure or to death. 



From the demands of natural selection results the intense prac- 

 ticality of the mental processes. Our senses tell us the truth as to 

 external nature, in so far as such phases of reality have been essen- 

 tial to the life of our ancestors. To a degree, they must have seen 

 "things as they really are," else they should not have lived to con- 

 tinue the generation. Our own individual ancestors through all the 

 ages have been creatures of adequate accuracy of sensation and of 

 adequate power of thought. Were it not so they could not have 

 coped with their environment. The sensations which their brains 

 translated into action contained enough of absolute reality to make 

 action safe. That our own ordinary sensations and our own induc- 

 tions from them are truthful in their essentials, is proved by the 

 fact that we have thus far safely trusted them. Science differs 

 from common sense mainly in the perfection of its tools. That the 

 instruments of precision used in science give us further phases of 

 reality is shown by the fact that we can trust our lives to them. We 

 find it safer to do so than to trust our unaided senses. 



While our senses tell us the truth as to familiar things, as rocks 

 and trees, foods and shelter, friends and enemies, they do not tell 

 us the whole truth : they go only so far as the demands of ancestral 

 environment have forced them to go. Chemical composition our 

 senses do not show. Objects too small to handle are too small to be 

 seen. Bodies too distant to be reached are never correctly appre- 

 hended. Accuracy of sense decreases as the square of the distance 

 increases. Sun and stars, clouds and sky, are in fact very different 

 from what they seem to the senses. 



In matters not vital to action, exactness of knowledge loses its 

 importance. Any kind of belief may be safe, if it is not to be carried 

 over into action. It is perfectly safe, in the ordinary affairs of life, 

 for one who does not propose to act on his convictions to believe in 

 witches and lucky stones, imps and elves, astral bodies and odic 

 forces. It is quite as consistent with ordinary living to accept these 

 as objective realities as it is to have the vague faith in microbes and 

 molecules, mahatmas and protoplasm, protective tariffs and mani- 

 fest destiny, which forms part of the mental outfit of the average 

 American citizen to-day. Unless these conceptions are to be brought 

 into terms of personal experience, unless in some degree we are to 

 trust our lives to them, unless they are to be wrought into action, 

 they are irrelevant to the conduct of life. As they are tested by 

 action, the truth is separated from the falsehood, and the error 

 involved in vague or silly ideas becomes manifest. As one comes 

 to handle microbes, they become as real as bullets or oranges and as 



