THE DISCOVERY OF LAWS 59 



it is not merely that I have more knowledge of it, but 

 that the knowledge is of a different kind. It is utterly 

 impossible that I should have of the one event the 

 kind of knowledge which I have of the other. If we 

 are to discuss profitably the problem before us, we must 

 remember this difference. We must not seek of events 

 which have not happened, the kind of knowledge appli- 

 cable only to those which have happened. And again, 

 we must not seek the kind of knowledge it is once more 

 a different kind that we have of purely logical or 

 internal propositions. When I say that a black cat 

 is black, I am quite certain that the statement is true 

 because by " a black cat " I mean a cat that is black ; 

 to say that a black cat is not black is not untrue ; it 

 is meaningless. The knowledge that I have of the 

 truth of the statement is necessarily different from that 

 which I can have of the statement that there is such a 

 thing as a black cat or that all cats are black ; and the 

 difference is once more in the kind of knowledge and 

 arises from a difference in the kind of statement ; it is 

 not a difference in degree of certainty. 



The problem would be expressed better if we merely 

 compared our knowledge of various future events and 

 asked why we are more certain that some will happen 

 than that others happen and how we arrive at this 

 superior knowledge, for then we are sure of comparing 

 always knowledge of the same kind. Of some future 

 events we are as certain as we can be in respect of know- 

 ledge of this kind ; we are as certain as we can be that 

 the sun will rise to-morrow. It would be ridiculous to 

 say that we are not certain because we do not feel towards 

 that prediction the same mental attitude that we feel 

 towards the assertion that the sun rose to-day or the asser- 

 tion that to-day is not to-morrow. For, once more, 

 the difference in mental attitude necessarily arises 

 from the difference in the nature of the statements. All 



