Dear List Members, I am looking for a formal definition of parsimony for fundamental scientific theories. From the tiny bit I understood of category theory, I had the impression it might provide the right framework for such a definition. The problem of motivating and defining parsimony is being discussed in analytic philosophy. An overview over the discussion can be found at http://plato.stanford.edu/entries/simplicity/ , which starts off with the sentences Most philosophers believe that, other things being equal, simpler theories are better. But what exactly does theoretical simplicity amount to? Syntactic simplicity, or elegance, measures the number and conciseness of the theories basic principles. Ontological simplicity, or parsimony, measures the number of kinds of entities postulated by the theory. One issue concerns how these two forms of simplicity relate to one another. I am interested in the "ontological simplicity, or parsimony". However, if one understands modern physics as describing essentially only one thing, the wave-function of the universe, then even the idea of defining parsimony in terms of numbers of kinds of things seems to be a bit odd. Yet, I think the idea is intuitively clear. The minimum requirement for a formal definition of parsimony is perhaps that it should identify theories such as the dynamics of Newtonian point-particles or the current "standard model" of particle physics as parsimonious, while the same theories with some oddities added, which do not themselves affect the "real" physics, should be identifiable as non-parsimonious. Beyond this, such a definition should presuppose as little as possible about the nature of the theories it applies to. Does somebody know about applications of category theory to this problem, or have an idea for who to do it? Cheers, Axel Rossberg --- Evolution and Ecology Program International Institute for Applied Systems Analysis Schlossplatz 1 A-2361 Laxenburg AUSTRIA ++++++++++++++++++++++++ reprints http://axel.rossberg.net/paper and more http://axel.rossberg.net