ON THE NOTION OF CAUSE 193 



the earlier event is the cause and the later event the 

 effect. 



Several considerations, however, make such special 

 sequences very different from the traditional relation of 

 cause and effect. In the first place, the sequence, in any 

 hitherto unobserved instance, is no more than probable, 

 whereas the relation of cause and effect was supposed to 

 be necessary. I do not mean by this merely that we are 

 not sure of having discovered a true case of cause and 

 effect ; I mean that, even when we have a case of cause 

 and effect in our present sense, all that is meant is that 

 on grounds of observation, it is probable that when one 

 occurs the other will also occur. Thus in our present 

 sense, A may be the cause of B even if there actually are 

 cases where B does not follow A. Striking a match will 

 be the cause of its igniting, in spite of the fact that some 

 matches are damp and fail to ignite. 



In the second place, it will not be assumed that every 

 event has some antecedent which is its cause in this 

 sense ; we shall only believe in causal sequences where 

 we find them, without any presumption that they always 

 are to be found. 



In the third place, any case of sufficiently frequent 

 sequence will be causal in our present sense ; for example, 

 we shall not refuse to say that night is the cause of day. 

 Our repugnance to saying this arises from the ease with 

 w iich we can imagine the sequence to fail, but owing to 

 the fact that cause and effect must be separated by a 

 finite interval of time, any such sequence might fail 

 through the interposition of other circumstances in the 

 interval. Mill, discussing this instance of night and day, 

 says : 



" It is necessary to our using the word cause, that we 

 should believe not only that the antecedent always has 



