2/8 DESIGN FOR A BRAIN 



blood. The intensity of faradisation will be continuously under 

 the experimenter's control. Not improbably it will be kept first 

 at zero and then increased. From a given instant the changes 

 in the variables will be recorded. 



In experimental psychology, the variables might be 4 the 

 number of mistakes made by a rat on a trial in a maze ' and 

 4 the amount of cerebral cortex which has been removed sur- 

 gically '. The second variable is permanently under the experi- 

 menter's control. The experimenter starts the experiment and 

 observes how the first variable changes with time while the 

 second variable is held constant, or caused to change in some 

 prescribed manner. 



While a single primary operation may seem to yield little 

 information, the power of the method lies in the fact that the 

 experimenter can repeat it with variations, and can relate the 

 different responses to the different variations. Thus, after one 

 primary operation the next may be varied in any of three ways : 

 the system may be changed by the inclusion of new variables 

 or by the omission of old ; the initial state may be changed ; 

 or the prescribed courses may be changed. By applying these 

 variations systematically, in different patterns and groupings, the 

 different responses may be interrelated to yield relations. 



By further orderly variations, these relations may be further 

 interrelated to yield secondary, or hyper-, relations ; and so on. 

 In this way the 4 machine ' may be made to yield more and more 

 complex information about its inner organisation. 



2/8. All our concepts will eventually be defined in terms of 

 this method. For example, ' environment ' is so defined in S. 3/8, 

 ' adaptation ' in S. 5/8, and ' stimulus ' in S. 6/6. If any have 

 been omitted it is by oversight ; for I hold that this procedure 

 is sufficient for their objective definition. 



The Field of a System 



2/9. The state of a system at a given instant is the set of numerical 

 values which its variables have at that instant. 



Thus, the six-variable system of S. 2/3 might at some 

 instant have the state: —4°, 0-3 radians/sec, 128°, 52 cm., 

 42-8 minutes, 88-4 cm. 



18 



