Let us start with the physical systems which apparently make up the universe. These range from the subatomic systems of atomic nuclei as described by physics, through the physical framework of this and other planets and the living systems observed on earth, to galactic systems at the other extreme. All these are natural systems, systems whose origin is in the origin of the universe and which are as they are as a result of the forces and processes which characterize this universe. They are systems which could not be other than they are, given a universe whose patterns and laws are not erratic.
There are also many other observed entities which are similar to natural systems in respects other than this last one: they could be other than they are. These are the systems which are the result of conscious design. They are the designed physical systems which man has made, the class stretching from hammers via tram cars to space rockets. They are designed as a result of some human purpose, which is their origin, and they exist to serve a purpose, even though, as in the case of an artist’s painting, for example, the purpose may be hard to define explicitly. But man’s design capability is not restricted to the construction of physical artefacts. We also see in the world a large number of what may be described as designed abstract systems such as mathematics or poems, or philosophies. They represent the ordered conscious product of the human mind. They are in themselves abstract systems, though thanks to previous successful design activity they can now be captured in designed physical systems such as books, films, records, blue prints. Again they will exist as a result of a positive act related to some objective — elucidation, maybe, or the enlargement of knowledge, or an inner urge to express the inexpressible. The human act of design is itself an example of a fourth possible system class: the human activity system. These are less tangible systems than natural and designed systems. Nevertheless, there are clearly observable in the world innumerable sets of human activities more or less consciously ordered in wholes as a result of some underlying purpose or mission. At one extreme is a system consisting of one man wielding a hammer, at the other the international political systems needed if life is to remain tolerable for the human race on this small planet. The range covered by this class of system is very large indeed. What every member of the class has in common is that it consists of a number of activities linked together as a result of some principle of coherency. This will as a minimum consist of the observer’s interest in viewing the set as a whole. For example, a dietitian might study the human activity system which consists of ‚the eating habits of the octogenarians of Basingstoke‘, in which case the people whose habits are studied will probably be unaware of their involvement with this system. Or an observer might take as a system a football team seeking to win a championship; here the team members will themselves know of their involvement as crucial to the system’s purpose, and will in fact have their own definitions of the purpose or mission which links the system’s activities and marks its boundary. The components of all such systems I take to be human activities. In the initial version of the typology (Checkland, 1971) these were combined with the natural and designed systems which will inevitably be closely linked to the human activity described—for example a ‚taking-leisure system‘ will consist of human activities involving various natural and designed physical and/or abstract systems such as playing fields, cricket bats, rules of games, etc. The research work has shown, however, that it is better to restrict the definition of the human activity system to the activities themselves, naming and describing other associated systems if appropriate at the time.
Beyond natural, designed physical, designed abstract, and human activity systems there has to be a category to include the systems beyond knowledge. Following Boulding we may term these transcendental systems. This completes a simple systems map of the universe which, as far as system classes is concerned, is itself complete. It is summarized in Figure 4. Any whole entity which an observer sees as a figure against the background of the rest of reality, may be described either as a system of one of these five classes or as a combination of systems selected from the five. Pursuing systems thinking becomes a matter of ascertaining the properties of systems of each class, and the way in which they combine and interact to form wider systems showing emergent properties. The long-term programme of the systems movement may be taken to be the search for conditions governing the existence of emergent properties and a spelling out of the relation between such properties and the wholes which exhibit them.