DESIGN FOR A BRAIN 



7/20 



particular value of S. A and B being full-functions, the represen- 

 tative point will move on curves in each plane, describing a line of 

 behaviour such as that drawn more heavily in the Figure. When 

 the line of behaviour meets the row of critical states at C — C, S 

 jumps to its other value, and the representative point continues 

 along the heavily marked line in the upper plane. In such a field 

 the movement of the representative point is everywhere state- 

 determined, for the number of lines from any point never exceeds 

 one. 



If, still dealing with the same real ' machine ', we ignore S, 

 and repeatedly form the field of the system composed of A and B 

 (S being free to take sometimes one value and sometimes the other), 

 we shall find that we get sometimes a field like I in Figure 7/20/2, 



1 A 



B B C 



Figure 7/20/2 : The two fields of the system composed of A and B. 

 P is in the same position in each field. 



and sometimes a field like II, the one or the other appearing 

 according to the value that S happens to have at the time. 



The behaviour of the system AB, in its apparent possession of 

 two fields, should be compared with that of the system described 

 in S. 6/3, where the use of two parameter- values also caused the 

 appearance of two fields. But in the earlier case the change of 

 the field was caused by the arbitrary action of the experimenter, 

 who forced the parameter to change value, while in this case the 

 change of the field of AB is caused by the inner mechanisms of the 

 ' machine ' itself. 



The property may now be stated in general terms. Suppose, 

 in a state-determined system, that some of the variables are due to 

 step-mechanisms, and that these are ignored while the remainder 

 (the main variables) are observed on many occasions by having 

 their field constructed. Then so long as no step-mechanism 



94 



