IHE BLACK BOX 6/22 



that it carries a + now is sufficient to allow prediction that the 

 machine's next state will be a 1. 



On the other hand, an observer who cannot observe the tape 

 can predict its behaviour only by reference to what was done to 

 the switch ten minutes ago. He will insist that the machine has 

 "memory". 



The two observers are not really in conflict, as we can see at once 

 when we reahse that they are talking of two "machines" that are not 

 identical. To the first observer, "the machine" means "calculator 

 + tape + switch"; to the second it means "calculator + switch". 

 They are talking about different systems. (Again it must be em- 

 phasised that in complex systems a mere reference to the material 

 object is often not sufficient to define adequately the system under 

 discussion.) (Compare S.6/14, 12/9.) 



Essentially the same difference can occur in a more biological 

 system. Thus, suppose I am in a friend's house and, as a car goes 

 past outside, his dog rushes to a corner of the room and cringes. 

 To me the behaviour is causeless and inexplicable. Then my friend 

 says, "He was run over by a car six months ago." The behaviour 

 is now accounted for by reference to an event of six months ago. 

 If we say that the dog shows "memory" we refer to much the same 

 fact — that his behaviour can be explained, not by reference to his 

 state now but to what his state was six months ago. If one is not 

 careful one says that the dog "has" memory, and then thinks of the 

 dog as having something, as he might have a patch of black hair. 

 One may then be tempted to start looking for the thing; and one 

 may discover that this "thing" has some very curious properties. 



Clearly, "memory" is not an objective something that a system 

 either does or does not possess; it is a concept that the observer 

 invokes to fill in the gap caused when part of the system is un- 

 observable. The fewer the observable variables, the more will the 

 observer be forced to regard events of the past as playing a part in 

 the system's behaviour. Thus "memory" in the brain is only 

 partly objective. No wonder its properties have sometimes been 

 found to be unusual or even paradoxical. Clearly the subject 

 requires thorough re-examination from first principles. 



117 



