DESIGN FOR A BRAIN 



a third arrow is added from tail to head, thus 



12/10 



X > z 



The rule is applied repeatedly till no further addition of arrows 

 is possible. Thus the diagram of immediate effects I in Figure 

 12/9/1 would yield the diagram of ultimate effects II. 



I 



>- 2 



K2 



I 



=^3 



Figure 12/9/1. 



The diagram of ultimate effects shows at once the dependencies 

 in the case when we allow time for the effects to work round the 

 system. Thus from II of the Figure we see that variable 1 is 

 permanently independent of 2, 3, and 4, and that the latter three 

 are all ultimately dependent on each other. 



The effects of constancy 



12/10. Suppose eight variables have been joined, by the method 

 of S. 6/6, to give the diagram of immediate effects shown in 

 Figure 12/10/1. We now ask: what behaviour at the three 



ABC 

 Figure 12/10/1. 



variables in B will make A and C independent, in the ultimate 

 sense, and also leave both A and C state-determined ? That is, 

 what behaviour at B will sever the whole into independent parts, 

 giving the diagram of immediate effects of Figure 12/10/2: 



164 



