THE AIM OF SCIENCE 53 



setting of eggs. There is a great deal of precise 

 measurement in physiology and psychology which 

 has led or is leading to exact science, though not 

 to mechanical re-description. 



Moreover, to return to a consideration referred 

 to in the section on reduction, we are very strongly 

 of opinion that Biology does not necessarily make 

 progress towards perfection by the mechanical 

 analysis of changes that go on in living bodies. 

 That kind of analysis or reduction to the lowest 

 terms is an engine of research which must be 

 worked for all it is worth, but it does not directly 

 answer any biological questions. For Biology 

 has a particular end that of describing the life 

 of plants and animals, and that end is not 

 necessarily achieved by discoveries in the physics 

 and chemistry of living bodies. We watch a 

 bird building its nest. We know that there is 

 an intricate sequence of physical and chemical 

 changes going on in its body. We feel sure that 

 nothing occurs that contradicts any of the es- 

 tablished laws of chemistry and physics. We 

 do not know whether a complete chemical and 

 physical description of what occurs is realizable 

 or not. We know that it has not been given. 

 But we feel sure that if it were given it would 

 not directly help us to understand the bird build- 

 ing its nest. For that requires a different kind 

 of description with different concepts, which 



