COEXISTENCES INDEPENDENT OF CAUSATION. 117 



5. It sometimes happens that a mere change in the 

 mode of verbally enunciating a question, though nothing is 

 really added to the meaning expressed, is of itself a consider 

 able step towards its solution. This, I think, happens in the 

 present instance. The degree of certainty of any generalization 

 which rests on no other evidence than the agreement, so far as 

 it goes, of all past observation, is but another phrase for the 

 degree of improbability that an exception, if any existed, 

 could have hitherto remained unobserved. The reason for 

 believing that all crows are black, is measured by the impro 

 bability that crows of any other colour should have existed to 

 the present time without our being aware of it. Let us state 

 the question in this last mode, and consider what is implied in 

 the supposition that there may be crows which are not black, 

 and under what conditions we can be justified in regarding 

 this as incredible. 



If there really exist crows which are not black, one of two 

 things must .be the fact. Either the circumstance of black 

 ness, in all crows hitherto observed, must be, as it were, an 

 accident, not connected with any distinction of Kind ; or if it 

 be a property of Kind, the crows which are not black must be 

 a new Kind, a Kind hitherto overlooked, though coming under 

 the same general description by which crows have hitherto 

 been characterized. The first supposition would be proved true 

 if we were to discover casually a white crow among black ones, 

 or if it were found that black crows sometimes turn white. 

 The second would be shown to be the fact if in Australia or 

 Central Africa a species or a race of white or grey crows were 

 found to exist. 



6. The former of these suppositions necessarily implies 

 that the colour is an effect of causation. If blackness, in 

 the crows in which it has been observed, be not a property 

 of Kind, but can be present or absent without any difference 

 generally in the properties of the object; then it is not 

 an ultimate fact in the individuals themselves, but is certainly 

 dependent on a cause. There are, no doubt, many properties 

 which vary from individual to individual of the same Kind, 



