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A command is a message which directly changes the state of the world
as far as the receiver of the message is concerned, i.e. the set
of possible actions for it.
Changing the state of the world the sender of a command can prevent the
receiver from doing something or open a possibility of doing
something new. The meaning of
a command is the way it changes the state of receiver. In the classical
limiting case a command leaves the receiver no choice at all, so that
the action of the receiver is uniquely determined by the command.
Computer languages can serve as an illustration of this kind of semantics.
Another example is control of a rocket from the earth. It involves
a certain language of electromagnetic signals sent to the rocket.
Here the command leaves almost no choice for the rocket,
because there is no absolute precision of the implementation of continuous
quantities. This situation is typical; what is meant by 'almost' is,
of course varying from case to case.
Copyright© 1991 Principia Cybernetica -
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