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I have to side with Klaus on this. I haven't ready Ashby, but I can think of 2 interpretations that might clear this up. 1. The complexity being modelled is limited to what is immediately pertinent to the fulfilment of some goal for the thing being 'regulated' by the agent. Limits here include the extent of the agent's capacity to regulate, and the goal of the regulation. 2. 'Systems' are just models anyways, so if the agent is seeking to regulate a 'system', the system is probably already simplified down to something that the agent can handle. Cheers. Fil Mattias Arvola wrote: > On Fri, 10 Oct 2008 15:31:13 -0400, Klaus Krippendorff > <[log in to unmask]> wrote: > >> you are saying that a theory must have more variety than what it > represents. just the opposite is the case. any theory reduces the variety > of phenomena to the variables it theorizes. the theory of free fall does > not say anything about aerodynamics and weather conditions of the > experiments conducted. > > Perhaps I can claryfy what Ashby meant by the law of requisite variety. For > a regulator to be able to control or regulate another system it needs to > have a model of that system/process that has more possible variety than the > system/process it is set to regulate. The reason is that the regulator, to > be able to control the process, it needs to be able to meet every > disturbance with at least one counteraction. Thus it needs to have more > variety than the process it is supposed to control. > > How we should translate this to theories I'm not sure. But I would expect > that if we want to explain or predict a phenomenon, we would need our theory > to be able to predict at least all states of the phenomenon: it would need > as much or more possible variety than the phenomenon it is supposed to > explain or predict. However, my memory and interpretation of Prof. Erik > Hollnagels cognitive system engineering classes may be faltering. > > Cheers, > // Matti Arvola -- Filippo A. Salustri, Ph.D., P.Eng. Department of Mechanical and Industrial Engineering Ryerson University 350 Victoria St, Toronto, ON, M5B 2K3, Canada Tel: 416/979-5000 ext 7749 Fax: 416/979-5265 Email: [log in to unmask] http://deseng.ryerson.ca/~fil/