164 INTRODUCTION TO SCIENCE 



can afford to act as if the only threads were 

 mechanical, but in truth it may be otherwise. 

 In the area which we call the biological order 

 the mechanical threads are continued, but they 

 are no longer dominant. In the area which we 

 call psychical the organic threads are continued, 

 but others form the pattern. As we pass from 

 inorganic to organic, from organic to psychical, 

 the mechanical warp becomes as it were less 

 important, and new aspects of Reality find freer 

 expression. But the metaphor is hopeless in its 

 suggestion of threads that are passively twisted 

 and interlaced. We have to think of living 

 threads, like those of some of the simplest 

 Protists which spin a changeful web. We have 

 to think of living threads that share in working 

 out the pattern of the web. 



SUMMARY. The aim of Science is the descrip- 

 tion of facts, the aim of Philosophy their interpre- 

 tation. There is much need for critical Metaphysics 

 to function as a sublime Logic, testing the complete- 

 ness and consistency of scientific descriptions, 

 whether of things as they are or of the way in which 

 they have come to be. On the other hand, meta- 

 physics should not reach forward to its constructive 

 system without taking account of the raw material 

 which the sciences furnish. The scientific account 

 of things is self-limited by the nature of its descrip- 

 tions: Only in mechanics can we say " The Cause 



