The Empirical Underdetermination of Theories

Antirealists believe that since observation is the only basis for factual knowledge, unobservable entities cannot be known. This is made evident by the empirical underdetermination of theories (see Stanford 2013): they are introduced as expla­nations of the observable phenomena, but for any set of given phenomena many incompatible explanations can be found; therefore, it is claimed, we cannot know which one is true.

The history of science, however, would seem to refute this argument: cases of actual competition among empirically equivalent theories have been very few, and eventually they have been decided to everybody's satisfaction (e.g., undulatory vs. corpuscular theory of light; Ptolemaic vs. Copernican vs. Tychonian cosmology). There are mathematically intertranslatable theories, like Newtonian mechanics (based on force) versus Lagrangian or Hamiltonian mechanics (based on a principle

of minimal action); or theories introducing fields and theories using action at dis­tance with retarded potentials (Putnam 1978b: 133), but they look more like dif­ferent formulations of the same theory. There seems to be a genuine conflict between Heisenberg’s matrix mechanics and Schrodinger’s wave mechanics (Put­nam 1978c: 555; Friedman 1983: 165 ff.; Fano 2005: 166), and between standard quantum mechanics and Bohmian mechanics; but one day we might find new empirical consequences which allow to decide between them. In general, “it has never been shown that for any theory there exist non trivial and minimally plausible alternatives” (Psillos 1999: 168); underdetermination does not look like a concrete problem in scientific practice, but a merely in-principle risk not to be taken too seriously (see Laudan and Leplin 1991, 1993).

Yet, isn’t it a logical fact that there are infinitely many possible theories com­patible with any body of data? So, it has been suggested that our failure to consider many of those theories (including perhaps the true one) has to do with our con­servatism and lack of imagination, and that many unconceived alternatives “exceed our grasp” (Stanford 2006).

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