3/4 DESIGN FOR A BRAIN 



such that the many variables are used throughout as one aggre- 

 gate which can take either of two forms. If, however, the 

 aggregate were split in the experiment, as would happen if we 

 recorded four classes of results : 



(1) in the animal house in summer 



(2) in the animal house in winter 



(3) in the open air in summer 



(4) in the open air in winter 



then we must either allow the variable ' condition of experiment ' 

 to take four values, or we could consider the experiment as 

 subject to two variables : ' site of experiment ' and ' season of 

 year ', each of which takes two values. According to this method, 

 what is important is not the material structure of the technical 

 devices but the experiment's logical structure. 



3/4. But is the method yet adequate ? Can all the living 

 organisms' more subtle qualities be numericised in this way ? On 

 this subject there has been much dispute, but we can avoid a part 

 of the controversy ; for here we are concerned only with certain 

 qualities defined. 



First, we shall be dealing not so much with qualities as with 

 behaviour : we shall be dealing, not with what an organism feels 

 or thinks, but with what it does. The omission of all subjective 

 aspects (S. 1/11) removes from the discussion the most subtle of 

 the qualities, while the restriction to overt behaviour makes the 

 specification by variable usually easy. Secondly, when the non- 

 mathematical reader thinks that there are some complex quantities 

 that cannot be adequately represented by number, he is apt 

 to think of their representation by a single variable. The use of 

 many variables, however, enables systems of considerable com- 

 plexity to be treated. Thus a complex system like ' the weather 

 over England ', which cannot be treated adequately by a single 

 variable, can, by the use of many variables, be treated as ade- 

 quately as we please. 



3/5. To illustrate the method for specifying the behaviour of a 

 system by variables, two examples will be given. They are of 

 little intrinsic interest ; more important is the fact that they 

 demonstrate that the method is exact and that it can be extended 

 to any extent without loss of precision. 



32 



