226 SCIENTIFIC METHOD IN PHILOSOPHY 



analogy with volition which makes us imagine that the 

 effect is compelled by it. A cause is an event or group 

 of events, of some known general character, and having 

 a known relation to some other event, called the effect ; 

 the relation being of such a kind that only one event, or 

 at any rate only one well-defined sort of event, can have 

 the relation to a given cause. It is customary only to 

 give the name " effect ' to an event which is later than 

 the cause, but there is no kind of reason for this restric- 

 tion. We shall do better to allow the effect to be before 

 the cause or simultaneous with it, because nothing of 

 any scientific importance depends upon its being after 

 the cause. 



If the inference from cause to effect is to be indubit- 

 able, it seems that the cause can hardly stop short of 

 the whole universe. So long as anything is left out, 

 something may be left out which alters the expected 

 result. But for practical and scientific purposes, phe- 

 nomena can be collected into groups which are causally 

 self-contained, or nearly so. In the common notion of 

 causation, the cause is a single event we say the lightning 

 causes the thunder, and so on. But it is difficult to 

 know what we mean by a single event ; and it generally 

 appears that, in order to have anything approaching 

 certainty concerning the effect, it is necessary to include 

 many more circumstances in the cause than unscientific 

 common sense would suppose. But often a probable 

 causal connection, where the cause is fairly simple, is of 

 more practical importance than a more indubitable con- 

 nection in which the cause is so complex as to be hard 

 to ascertain. 



To sum up : the strict, certain, universal law of causa- 

 tion which philosophers advocate is an ideal, possibly 

 true, but not known to be true in virtue of any avail- 



