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Systems thinking and practice
Systems thinking and practice

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5.3 Summary

The brief definition of a system is set of components interconnected for a purpose. Joseph O'Connor and Ian McDermott (1997) distinguish a system from a heap using the longer definition as follows:

A systemA heap
Interconnecting parts functioning as a wholeA collection of parts
Changed if you take away pieces or add more pieces. If you cut the system in half you do not get two smaller systems, but a damaged system that will not properly functionEssential properties are unchanged whether you add or take away pieces. when you halve a heap, you get two smaller heaps
The arrangement of the pieces is crucialThe arrangement of the pieces is irrelevant
The parts are connected and work togetherThe parts are not connected and can function separately
Its behaviour depends on the total structure. Change the structure and the behaviour changesIts behaviour (if any) depends on its size or on the number of pieces in the heap.
(O'Connor and McDermott, 1997, p. 3)

I have also used the word ‘system’ to make five points about thinking in terms of systems:

  1. The intangible elements, e.g. norms and assumptions, are essential factors in understanding how a system works.

  2. The boundary of a system need not correspond with recognised departmental, institutional or other ‘physical’ boundaries. Explanatory systems are identified in relation to the observer's interests.

  3. Often one has to extend the boundary (take a helicopter view) in order to achieve a coherent understanding of a complex situation.

  4. A system at one level of analysis can be viewed instead as a sub-system in its environment at a higher level of analysis.

  5. Models and analogies of systems are powerful tools in helping to identify patterns and regularities.


Which of the following do you recognise as a system, according to the definitions given above?

  1. The houses in an old village.

  2. Your personal computer.

  3. Activities needed to get this course to you on time.

  4. A small wood.

  5. The spare parts in the store of a garage.

  6. Mathematics.

  7. Meetings of the board of directors of a company.


Numbers 2, 3 and 6 appear straightforward; all have a set of components interconnected for a purpose. In one case the components are objects, in another activities and in the third they are ideas, but they are all familiarly called systems.

However, these only become systems if we have an interest in doing something with them. The personal computer or laptop on your desk is not a sytem until you take an interest in it, by, for example, using it ti do your assignments, or until an engineer comes to repair it when it is not working properly. Numbers 4 and 7 are not usually called sytems, and it may seem a bit strange to call them so. But they fit the definition given in the text, and as you will see, there are real advatages in using the concept of a system in these kinds of cases. With the wood, it makes sense to speak as if it had the purpose of enabling plants to grow, birds to nest and feed and so on. In case of the Board meeting, it makes sense to speak as if it had the purpose of making decisions about the running of the company (doing so might reveal the fact that a particular Board doesn't in fact make the important decisions).

Numbers 1 and 5, as described in the question, aren't systems. In neither case are the components necessarily interconnected for a purpose, they are more akin to a collection of things. Of course, only a small change in the description could make a big difference. A storekeeper dishing out the spare parts looks like a system. So would the houses, if I included the services which link them or the activities of the people living in them.