INTRODUCTION xiii 



physical research as altogether separate from the familiar 

 table, without prejudging the question of their ultimate 

 identification. It is true that the whole scientific 

 inquiry starts from the familiar world and in the end it 

 must return to the familiar world; but the part of the 

 journey over which the physicist has charge is in foreign 

 territory. 



Until recently there was a much closer linkage; the 

 physicist used to borrow the raw material of his world 

 from the familiar world, but he does so no longer. His 

 raw materials are aether, electrons, quanta, potentials, 

 Hamiltonian functions, etc., and he is nowadays scrupu- 

 lously careful to guard these from contamination by con- 

 ceptions borrowed from the other world. There is a 

 familiar table parallel to the scientific table, but there is 

 no familiar electron, quantum or potential parallel to the 

 scientific electron, quantum or potential. We do not even 

 desire to manufacture a familiar counterpart to these 

 things or, as we should commonly say, to "explain" the 

 electron. After the physicist has quite finished his world- 

 building a linkage or identification is allowed; but prema- 

 ture attempts at linkage have been found to be entirely 

 mischievous. 



Science aims at constructing a world which shall be 

 symbolic of the world of commonplace experience. It 

 is not at all necessary that every individual symbol that 

 is used should represent something in common experi- 

 ence or even something explicable in terms of com- 

 mon experience. The man in the street is always mak- 

 ing this demand for concrete explanation of the things 

 referred to in science; but of necessity he must be 

 disappointed. It is like our experience in learning to 

 read. That which is written in a book is symbolic of a 

 story in real life. The whole intention of the book is 



