HYPOTHESES. 5 



every phenomenon of colour. But although this, if 

 proved, would be an important extension of our 

 knowledge of nature, it would not explain how or 

 why a motion, or a chemical action, should produce 

 a sensation of colour ; and however diligent might be 

 our scrutiny of the phenomena, whatever number of 

 hidden links we might detect in the chain of causa- 

 tion terminating in the colour, the last link would 

 still be a law of colour, not a law of motion, nor of 

 any other phenomenon whatever. Nor does this 

 observation apply only to colour, as compared with 

 any other of the great classes of sensations ; it applies 

 to every particular colour, as compared with others. 

 White colour can in no manner be explained exclu- 

 sively by the laws of the production of red colour. In 

 any attempt to explain it, we cannot but introduce, as 

 one element of the explanation, the proposition that 

 some antecedent or other produces the sensation of 

 white. 



The ideal limit, therefore, of the explanation of 

 natural phenomena (towards which as towards other 

 ideal limits we are constantly tending, without the 

 prospect of ever completely attaining it,) would be to 

 show that each distinguishable variety of our sensa- 

 tions, or other states of consciousness, has only one 

 sort of cause; that, for example, whenever we per- 

 ceive a white colour, there is some one condition or 

 set t)f conditions which is always present, and the 

 presence of which always produces in us that sensa- 

 tion. As long as there are several known modes of 

 production of a phenomenon, (several different sub- 

 stances, for instance, which have the property of 

 whiteness, and between which we cannot trace any 

 other resemblance) , so long it is not impossible that 

 one of these modes of production may be resolved into 



