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The Nature of a System

On the Mismatch Between Systems and Their Models by Russell Ackoff defines a system:

  1. A system is a whole that is defined by its function(s) in one or more containing systems.
  2. Every system contains at least two essential parts and these must satisfy three conditions.
    1. Every essential part of a system can affect its behavior or properties.
    2. The way an essential part affects the properties or behavior of the whole depends on the state or activity of at least one other part of the system.
    3. Groups of essential parts, subsystems, also can affect the behavior and properties of the whole system and none has an independent effect on it.

Some important properties of a system derive from its definition.

  • When a system is taken apart it loses its essential properties.
  • No part of a system can carry out the function that defines the system.
  • When a system is taken apart its essential parts lose their ability to carry out the function they have in the whole.


  • When the performance of any essential part of a system, taken separately, is improved, the performance of the whole may not be.