Realism, rationalism and scientific method: Introduction: scientific realism and philosophical realism

philosophical theory has been found to conflict with scientific practice does not mean that the practice is without a guide. Incommensurability only shows that scientific discourse which contains detailed and highly sophisticated discussions concerning the comparative advantages of paradigms obeys laws and standards that have little in common with the naive models that philosophers of science have constructed for that purpose. ' Cf. vol. 2, ch. 7 and part 1 of SFS as well as vol. 2, ch. 1. 38 All the existing attempts to overcome incommensurability in the sense just described assume that the concepts of the systems to be connected can be used at the same time, and that the only problem is how to establish relations between them. But the example I explained in ch. 17 of A M and the relation between relativity and classical physics which shows similar features (cf. the appendix to ch. 8 of vol. 2) show that there are cases which do not agree with this assumption. There exist pairs of theories (world views; forms of life) such that using terms in accordance with the rules of the one theory (world view; form of life) makes it impossible to construct and even to think of the concepts that arise when terms are used in accordance with the rules of the other theory (world view; form of life). Logicians have not yet found any remedy for dealing with this situation and there is no need to, for the practice of science is not hindered by it. The only difficulty that arises is for certain abstract semantical views. 39 For details on 'crucial experiments' cf. vol. 2, ch. 8.9, 8.10 as well as A M, 282ff. Moreover, there are formal criteria: a linear theory (theory with linear differential equations as basic equations) is preferable to non-linear theories because solutions can be obtained much more easily. This was one of the main arguments against the non-linear electrodynamics of Mie, Born and Infeld. The argument was also used against the general theory of relativity until the development of high speed computers simplified numerical calculations. Or, a 'coherent' account is preferable to a non-coherent one (this was one of Einstein's main criteria in favour of his approach). A theory using many and daring approximations to reach its 'facts' is, to some, much less likeable than a theory that uses only a few safe approximations. Number of facts predicted may be another criterion. Non-formal criteria usually demand conformity with basic theory (relativisticinvariance; agreement with the quantum laws) or with metaphysical principles (such as Einstein's 'principle of reality' or his principle that physical entities such as space which have effects must also be capable of being affected). It is interesting to see that the criteria often give conflicting results so that a choice becomes necessary.