ON THE NOTION OF CAUSE 217 



uniformities of sequence or coexistence. After lightning 

 comes thunder, after a blow received comes pain, after 

 approaching a fire comes warmth ; again, there are uni- 

 formities of coexistence, for example between touch and 

 sight, between certain sensations in the throat and the 

 sound of one's own voice, and so on. Every such 

 uniformity of sequence or coexistence, after it has been 

 experienced a certain number of times, is followed by an 

 expectation that it will be repeated on future occasions, 

 i.e. that where one of the correlated events is found, the 

 other will be found also. The connection of experienced 

 past uniformity with expectation as to the future is just 

 one of those uniformities of sequence which we have 

 observed to be true hitherto. This affords a psycho- 

 logical account of what may be called the animal belief in 

 causation, because it is something which can be observed 

 in horses and dogs, and is rather a habit of acting than 

 a real belief. So far, we have merely repeated Hume, 

 who carried the discussion of cause up to this point, 

 but did not, apparently, perceive how much remained 

 to be said. 



Is there, in fact, any characteristic, such as might be 

 called causality or uniformity, which is found to hold 

 throughout the observed past ? And if so, how is it to 

 be stated ? 



The particular uniformities which we mentioned before, 

 such as lightning being followed by thunder, are not 

 found to be free from exceptions. We sometimes see 

 lightning without hearing thunder ; and although, in 

 such a case, we suppose that thunder might have been 

 heard if we had been nearer to the lightning, that is a 

 supposition based on theory, and therefore incapable of 

 being invoked to support the theory. What does seem, 

 however, to be shown by scientific experience is_ this : 



