4o8 The Inward Urge to Change 



Modern science has for the most part avoided this type 

 of interpretation of events observed in the physical and 

 chemical materials and processes. We have learned, that is, 

 to give what is called a mechanistic account of what our 

 eyes have seen. We do not say that the apple falls from the 

 tree because it has a certain affection or attraction for the 

 earth. We accept the fact that things " fall " and we meas- 

 ure the velocities and the forces of falling and so build up 

 a set of " laws " of gravitation. We do not say that an 

 acid neutralizes a base because of any inherent attraction or 

 hostility. When we do use such terms, we are aware (or 

 shovdd be) that we are speaking metaphorically. We at- 

 tempt to analyze and measure and describe as objectively 

 as possible. We have developed a mode of thinking of events 

 in such relatively simple terms as are employed in mechanics: 

 pushes and pulls of various degrees, with consequent move- 

 ments of masses of matter, in specified directions, at meas- 

 urable velocities. We have learned that this method gives 

 ^^s reliable results in dealing with many systems of material 

 things. Although we do not know very much about the 

 nature of the various kinds of ** energy," we find it satis- 

 factory to assume that they are interchangeable and fixed 

 in amounts. We find it satisfactory to " explain " many 

 kinds of events in terms of energy and matter — that is, in 

 terms of mechanism. 



Mechanism and Origins 



These two modes of explaining may be thought of 

 as being respectively an approach from above and an ap- 

 proach from below. Let us take a familiar example. After 

 one engages in brisk exercise, the heart beats faster: this is 

 a fact. We may explain it by saying that there is need for 

 more oxygen, or for more rapid elimination of carbon di- 

 oxid. Or we may explain the fact by saying that the change 

 in the chemical condition of the blood accelerates the heart 

 through a special action upon a certain nerve center. In one 



