56 COSMIC PHILOSOPHY. [pi. L 



of conceptions, of which the conception of blackness is not 

 the one upon which the specific identity of the sum-total 

 depends. We have had experience of bay and of sorrel 

 horses, of black and of white bears, of grey and of tortoise- 

 shell cats ; and, in accordance with such experience, we 

 find it perfectly easy to regard any other animal as varying 

 colour while retaining its specific identity. Our belief that 

 all crows are black rests, therefore, upon purely negative 

 evidence, — upon the absence of any experience of crows that 

 are not black ; and no amount of negative evidence can out- 

 weigh a single well-established item of positive evidence. 



Quite otherwise would it be if our explorer should assert 

 that he had discovered crows destitute of a vertebrate 

 skeleton. We should reply, with confidence, that in the 

 absence of such a skeleton the animal in question could not 

 have been a crow. And the justice of the reply becomes 

 apparent when we turn to the case of the nitrogen, where 

 the conditions are so simple that we can keep them all in 

 mind at once, and where we can imagine no variation which 

 shall not at once alter the whole character of the case. We 

 cannot imagine nitrogen supporting combustion, for as soon 

 as it did so it would cease to be nitrogen. That A is A, is an 

 identical proposition only when the attributes of A are 

 constant. Now the incapacity to support combustion is one 

 of the attributes by the possession of which nitrogen is 

 nitrogen. And to say that nitrogen may at some future time 

 support combustion, is to say that a will cease to be a, and 

 become something else. 



Now, why are we compelled to think thus ? Because we 

 are incapable of transcending our experience. Our experience 

 of nitrogen is that it will not support combustion, and we 

 are incapable of imagining it to be otherwise in contradic- 

 tion to our experience. Our conception of nitrogen, formed 

 by experience, is that of a substance which will not support 

 combustion, and we cannot mentally sever the substance 



