SCIENCE AS A SYMBOL AND A LAW 13 



to revision because of the discovery of new phe- 

 nomena. 



Two methods of framing a physical theory may be 

 distinguished. They may be termed the abstractive and 

 the hypothetical methods. 



According to the abstractive method, a class of ob- 

 jects or phenomena is described and a name or symbol 

 assigned to that assemblage of properties common to 

 all the objects or phenomena composing the class, as 

 perceived by the senses, and without introducing any- 

 thing hypothetical. 



There is only one example of a complete physical 

 theory formed exclusively from the data of experience 

 by the abstractive method, the principles of the sci- 

 ence of mechanics. The objects discussed in mechanics 

 are material and real bodies, all of which possess the 

 sensible properties of occupying space and resisting 

 change of motion. The phenomena dealt with are 

 confined to those attributes of matter distinguished by 

 the words force and motion, which we have found to 

 be common to all bodies of which we have any knowl- 

 edge. And the laws deduced follow from axioms and 

 definitions which express this universal experience. 



According to the hypothetical method, the existence 

 of a class of fictitious objects or phenomena, which can- 

 not be perceived by the senses, is assumed. And prop- 

 erties are assigned to them, similar to those known to 

 be true of a class of real objects or phenomena, which 



