182 INDUCTION. 



dispute. Assertions for which there is abundant 

 positive evidence are often disbelieved, on account of 

 what is called their improbability, or impossibility. And 

 the question for consideration is, what, in the present 

 case, these words mean, and how far and under what 

 circumstances the properties which they express are 

 sufficient grounds for disbelief. 



2. It is to be remarked in the first place, that 

 the positive evidence produced in support of an 

 assertion which is nevertheless rejected on the 

 score of impossibility or improbability, is never such 

 as amounts to full proof. It is always grounded upon 

 some approximate generalization. The fact may 

 have been asserted by a hundred witnesses; but 

 there are many exceptions to the universality of the 

 generalization that what a hundred witnesses affirm is 

 true. We may seem to ourselves to have actually 

 seen the fact : but, that we really see what we think 

 we see, is by no means an universal truth ; our organs 

 may have been in a morbid state, or we may have 

 inferred something, and imagined that we perceived it. 

 The evidence, then, in the affirmative, being never 

 more than an approximate generalization, all will 

 depend upon what the evidence in the. negative is. 

 If that also rests upon an approximate generalization, 

 it is a case for comparison of probabilities. If the 

 approximate generalizations leading to the affirmative 

 are, when added together, less strong, or in other 

 words, further removed from universality, than the 

 approximate generalizations which support the nega- 

 tive side of the question, the proposition is said to be 

 improbable, and is to be disbelieved, provisionally. 

 If however an alleged fact be in contradiction, not to 

 any number of approximate generalizations, but to a 



