76 WHAT IS SCIENCE? 



a law of one of these types into several laws of the same 

 type, or by changing it to a law of another known type. 

 And what are these types ? To answer that question 

 would be to expound all science ; I want only to encour- 

 age the reader to study science for himself and to find 

 the types. But I have already indicated some of the 

 more important types, such as the law of a substance, 

 the law of a particular kind of animal and the numerical 

 law ; and it has been urged that all these laws have the 

 important common feature that the things between which 

 they assert invariable associations are themselves inter- 

 connected by other laws. Those who have previously 

 read in the philosophy of science will be surprised that 

 the causal law is omitted, but the reasons of the omission 

 were given in the previous chapter. In physics, at least, 

 it is not an important type, though it possibly may be 

 in other sciences, such as meteorology and medicine. And 

 by omitting the causal laws, we can omit also all reference 

 to the " Canons of Induction " which were supposed by 

 an earlier generation to provide the one and only means 

 for discovering scientific laws. They are futile, because 

 the problem which they profess to solve is not one which 

 has ever troubled any intelligent person. They tell us 

 how, when we know that an event is the cause or effect 

 of another, we may discover of which other event it is 

 the cause or the effect ; as a matter of fact, the crudest 

 common sense, applied in everyday life, serves for the 

 purpose. We might similarly draw up canons for dis- 

 covering of what substance a given property is a property, 

 when it is once known that it is a property of some sub- 

 stance ; but here again the rules would be so obvious as 

 not to be worth formulating. The problem of science is 

 not to discover examples of laws when once we know what 

 kind of law to look for ; it is to know for what kind of law 

 to look. And that problem, as we have insisted before, 

 is insoluble except by the genius which knows no rule. 



