244 THE PRINCIPLES OF SCIENCE. 



the most rudimentary notion of what constitutes reasoning 

 and science. 



At the same time there can be no doubt that practi- 

 cally what we find to be true of many similar objects will 

 probably be true of the next similar object. This is the 

 result to which an analysis of the Inverse Method of 

 Probabilities leads us, and, in the absence of any precise 

 data from which we may calculate probabilities, we are] 

 usually obliged to make a rough assumption that similars 

 in some respects are similars in other respects. Thus it \ 

 comes to pass that a very large part of the reasoning' 

 processes in which scientific men are engaged, seems toj 

 consist in detecting similarities between objects, and then; 

 rudely assuming that the like similarities will be detected! 

 in other cases. 



Distinction of Generalization and Analogy. 



There is no distinction but that of degree between what 

 is known as reasoning by generalization and reasoning by 

 analogy. In both cases from certain observed resemblances 

 we infer, with more or less probability, the existence of 

 other resemblances. In generalization the resemblances 

 have great extension and usually little intension, whereas 

 in analogy we rely upon the great intension, the extension 

 being of small amount (vol. i. p. 31). If we find that the 

 qualities A and B are associated together in a great 

 many instances, and have never been found separate, it is 

 highly probable that on the next occasion when we meet 

 with A, B will also be found to be present, and vice versa. 

 Thus wherever we meet with an object possessing gravity, 

 it is found to possess inertia also, nor have we met with 

 any material objects possessing inertia without discovering 

 that they also possess gravity. The probability has there 

 fore become very great, as indicated by the rules founded 



