"A mechanism showing a step function as its main characteristic" (W.R. ASHBY, 1960, p.91).
This term was suggested to ASHBY by J.C. WISDOM.
Systems endowed with a step mechanism are able to switch their behavior from one field of activity to another one. ASHBY explain this in the following way: "Suppose, in a state-determined system, that some of the variables are due to step-mechanisms, and that these are ignored while the remainder (the main variables) are observed on many occasions by having their field constructed. Then, so long as no step-mechanism changes value during the construction, the main variables will be found to form a state-determined system, and to have a definite field. But on different occasions different fields may appear" (p.94-5).
"If the system had contained two step-mechanism, each of two values, there would have been four fields of the main variables. In general, n steps-mechanism, each of two values, will give 2 fields. A moderate number of step mechanism may thus give a very much larger number of fields" (p.95).
So, step-mechanism in systems explain how they remain stable ("ultrastable in ASHBY's vocabulary) in a wide general deterministic sense, while however being able to adapt to a considerable range of variations, many times in a seemingly random way. Step-mechanism seem to open the way to heterogeneity and complexity.
For changes of field in an ultrastable system by switching at critical states through step-mechanisms, see ASHBY, 1960, p.96; figure 7/23/1.
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Bertalanffy Center for the Study of Systems Science (2020). Title of the entry. In Charles François (Ed.), International Encyclopedia of Systems and Cybernetics (2). Retrieved from www.systemspedia.org/[full/url]
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