1/14 THE PROBLEM 



The sole reason admitted for the behaviour of any part will be 

 of the form that its own state and the condition of its immediate 

 surroundings led, in accordance with the usual laws of matter, 

 to the observed behaviour. 



1/12. The ' operational ' method will be followed; so no psycho- 

 logical concept will be used unless it can be shown in objective 

 form in non-living systems; and when used it will be considered 

 to refer solely to its objective form. Related is the restriction 

 that every concept used must be capable of objective demonstra- 

 tion. In the study of Man this restriction raises formidable 

 difficulties extending from the practical to the metaphysical. 

 But as most of the discussion will be concerned with the observed 

 behaviour of animals and machines, the peculiar difficulties will 

 seldom arise. 



1/13. No teleological explanation for behaviour will be used. It 

 will be assumed throughout that a machine or an animal behaved 

 in a certain way at a certain moment because its physical and 

 chemical nature at that moment allowed it no other action. Never 

 will we use the explanation that the action is performed because 

 it will later be advantageous to the animal. Any such explanation 

 would, of course, involve a circular argument; for our purpose 

 is to explain the origin of behaviour which appears to be teleo- 

 logically directed. 



1/14. It will be further assumed (except where the contrary is 

 stated explicitly) that the fuctioning units of the nervous system, 

 and of the environment, behave in a determinate way. By this 

 I mean that each part, if in a particular state internally and affected 

 by particular conditions externally, will behave in one way only, 

 (This is the determinacy shown, for instance, by the relays and 

 other parts of a telephone exchange.) It should be noticed that 

 we are not assuming that the ultimate units are determinate, for 

 these are atoms, which are known to behave in an essentially 

 indeterminate way; what we shall assume is that the significant 

 unit is determinate. The significant unit (e.g. the relay, the 

 current of several milliamperes, the neuron) is usually of a size 

 much larger than the atomic so that only the average property 

 of many atoms is significant. These averages are often determinate 



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