THE LAWS OF SCIENCE 49 



is important because it gives a reason why we do actually 

 select for the study of science those portions of experience 

 which are actually selected ; but it is not the criterion 

 which we consciously apply. The conscious criterion 

 for the subject-matter of science is rather that it has been 

 regarded hitherto as connected together by a relation ) 



of invariable_association such as is asserted by a law. / 



I 



DO LAWS STATE CAUSES AND EFFECTS ? 



So far we have only considered half of the problem of 

 the laws of science. We have expanded and made more 

 precise the conception of a law of nature, have considered 

 why such laws are of such supreme importance for science, 

 and have inquired how they can be at once its starting 

 point and its goal. A law, we have concluded, is the^ 

 assertaijofjm^^ the events or 



properties or otheFThings that it declares to be invariajiy 

 associated are themselves collections of ..other invariably 

 ^^K^^BHngs. But we have not attempted to ask 

 furthefwliat is meant by " invariable association." We 

 noticed in passing at the outset that it was often thought 

 that laws were concerned characteristically with rela- 

 tions of cause and effect. A cause and its effect are invari- 

 ably associated. The view is therefore suggested that 

 by invariable association we mean simply the relation of 

 a cause to its effect. Is that what we mean ? This is 

 the other half of our problem and to it the rest of the 

 chapter must be devoted. 



We must naturally start by asking ourselves what 

 exactly we mean (or what we should mean) by " cause 

 and effect." This is a matter on which there has been 

 much discussion ; but the idea which underlies most 

 frequently the use of the terms seems to be this. We 

 imagine that whenever an event B happens, it happens 

 only because it has been preceded by some other event 



4 



