CHAPTER IV 

 THE DISCOVERY OF LAWS 



STATEMENT OF THE PROBLEM 



FOR now, having decided what laws are and 

 what they state, we have to ask how they are 

 discovered. Laws state invariable associations ; 

 but how can we ever be "sure that an association 

 is invariable ? We may have observed an association 

 many times, and have always found that if one of the 

 associated events or properties occurs, the other occurs 

 also ; but if the association is truly invariable, we must 

 know, not only that the association always has been found 

 in the past, but also that it always will be found in the 

 future. Moreover, even if we have found the association 

 every time in the past that w r e have looked for it, we 

 clearly cannot know that it has occurred when we have 

 not looked for it. The establishment that an association 

 is invariable and the assertion by a law that it is invariable 

 clearly require that we should be able to judge from the 

 observation of one or several occurrences of it all the 

 other occurrences that may happen or have happened. 

 How can we possibly attain such knowledge ? 



One answer to this question is simply that we do not 

 know. We can never be certain that an event will 

 happen in the same way that we are certain that it has 

 happened. Indeed, there is a difference in the sense of 

 the word " know " applied to the two cases a difference 

 in sense which is reflected by the use of different words 

 in most languages. When I have actually experienced 

 an event I have a direct and immediate perception of 

 it which is different in kind, and not merely in degree, 

 from my belief, however confident, that it will happen ; 



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