224 POPULAR SCIENCE MONTHLY 



Ancient logic was also familiar with this method of reasoning; 

 but it was branded with the name of incomplete induction as the worst 

 of all because it lacks absolute and unconditional certainty. One must 

 admit, however, that all contemporary science makes use of no form of 

 reasoning other than incomplete induction. It alone permits of pre- 

 diction, that is to say, the determination of relations which have not 

 yet been directly observed. 



But how does science get along with this lack of certainty in its 

 method of drawing conclusions ? The reply to this question is that the 

 probability of the conclusions may run the gamut of all possible grada- 

 tions from mere supposition to the maximum of probability which is 

 no longer to be distinguished, practically, from certainty. The prob- 

 ability is greater the more frequently any given incomplete induction of 

 this kind has been found consistent with subsequent experience. Thus 

 we have at our disposal a number of propositions which in their sim- 

 plest and most general shape take the form: If the component A is 

 to be found in a given thing, the component B is also to be found in it 

 (in relation to either time or space). 



If the relation is one of time, we term this general proposition the 

 law of causality. If it is one of space we speak of the idea (in the 

 Platonic sense) or type of the thing, of substance, etc. 



These considerations yield answers to many questions which have 

 been repeatedly propounded in various forms. We have first the ques- 

 tion of the universal validity of the law of causality. All attempts to 

 establish this kind of validity have failed, and only the fact remains 

 that without this law we should feel an unendurable uncertainty as to 

 the world. Hence it follows that we have to deal in this matter with a 

 question of fitness. From the constant stream of our experience we 

 select relations which we encounter again and again in order that when- 

 ever the component A is given us we may conclude that the component 

 B is also to be found. Hence we do not find these correlations occur- 

 ring as ' given,' but we ourselves bring them into our experiences, by 

 ourselves regarding the components which show such a connection as 

 belonging together. 



We may make quite the same statements in regard to space rela- 

 tions. The components which are always, or at any rate frequently, 

 encountered together we interpret as forming a unit; and we shape 

 from them a concept which includes these components. As in the case 

 of time relation, there is no sense in propounding the question why. 

 There are thousands of correlations to which we pay no attention be- 

 cause they are unique or rare. Knowledge of such a unique correla- 

 tion leads to nothing, because it does not enable us to infer the pres- 

 ence of one component from the presence of another and therefore does 

 not render prediction possible. Of all possible and actual combina- 



