296 CAUSATION 



symmetrical causal relation which is the same viewed 

 from either end. 



Primary physics postulates a strictly causal scheme, 

 but the causality is a symmetrical relation and not the 

 one-way relation of cause and effect. Secondary physics 

 can distinguish cause and effect but its foundation does 

 not rest on a causal scheme and it is indifferent as to 

 whether or not strict causality prevails. 



The lever in a signal box is moved and the signal 

 drops. We can point out the relation of constraint 

 which associates the positions of lever and signal; we 

 can also find that the movements are not synchronous, 

 and calculate the time-difference. But the laws of 

 mechanics do not ascribe an absolute sign to this time- 

 difference; so far as they are concerned we may quite 

 well suppose that the drop of the signal causes the motion 

 of the lever. To settle which is the cause, we have two 

 options. We can appeal to the signalman who is con- 

 fident that he made the mental decision to pull the lever; 

 but this criterion will only be valid if we agree that there 

 was a genuine decision between two possible courses 

 and not a mere mental registration of what was already 

 predetermined. Or we can appeal to secondary law 

 which takes note of the fact that there was more of the 

 random element in the world when the signal dropped 

 than when the lever moved. But the feature of secon- 

 dary law is that it ignores strict causation; it concerns 

 itself not with what must happen but with what is 

 likely to happen. Thus distinction of cause and effect 

 has no meaning in the closed system of primary laws 

 of physics; to get at it we have to break into the scheme, 

 introducing considerations of volition or of probability 

 which are foreign to it. This is rather analogous to the 

 ten vanishing coefficients of curvature which could only 



