7/9 DESIGN FOR A BRAIN 



The behaviour of the system A B, 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 A B is caused by the inner mechanisms of the 

 4 machine ' itself. 



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

 in an absolute system, that some of the variables are step-functions, 

 and that these are ignored while the remainder (the main variables) 

 are observed on many occasions by having their field constructed. 



I 



B 



Figure 7/8/2 : The two fields of the system composed of A and B. 

 P is in the same position in each field. 



Then so long as no step-function changes value during the con- 

 struction, the main variables will be found to form an absolute 

 system, and to have a definite field. But on different occasions 

 different fields may be found. The number of different fields shown 

 by the main variables is equal to the number of combinations of 

 values provided by the step-functions. 



1J9. These considerations throw light on an old problem in the 

 theory of mechanisms. 



Can a ' machine ' be at once determinate and capable of spon- 

 taneous change ? The question would be contradictory if posed 

 by one person, but it exists in fact because, when talking of living 

 organisms, one school maintains that they are strictly determinate 

 while another school maintains that they are capable of spon- 

 taneous change. Can the schools be reconciled ? 



88 



