The fundamental questions in regulation and control can be answered only when we are able to consider the broader set of what it might do, when “migh… - W. Ross Ashby

The most fundamental concept in cybernetics is that of "difference", either that two things are recognisably different or that one thing has changed with time. Its range of application need not be described now, for the subsequent chapters will illustrate the range abundantly. All the changes that may occur with time are naturally included, for when plants grow and planets age and machines move some change from one state to another is implicit. So our first task will be to develop this concept of "change", not only making it more precise but making it richer, converting it to a form that experience has shown to be necessary if significant developments are to be made.

By a state of a system is meant any well-defined condition or property that can be recognised if it occurs again. Every system will naturally have many possible states.

When a constraint exists advantage can usually be taken of it.