The underdetermination of theory by evidence must be distinguished from holism. The latter is a doctrine about the testing of scientific hypotheses; the former is a thesis about empirically adequate logically incompatible global theories or "systems of the world". The distinction is crucial for an adequate assessment of the underdetermination thesis. The paper shows how some treatments of underdetermination are vitiated by failure to observe this distinction, and identifies some necessary conditions for the existence of multiple empirically equivalent global theories. (...) We consider how empiricists should respond to the possibility of such systems of the world. (shrink)

The instrumentalist argument from the underdetermination of theories by data runs as follows: (1) every theory has empirically equivalent rivals; (2) the only warrant for believing one theory over another is its possession of a greater measure of empirical virtue; (3) therefore belief in any theory is arbitrary. In this paper, I examine the status of the first premise. Several arguments against the universal availability of empirically equivalent theoretical rivals are criticized, and four algorithms for producing empirically equivalent rivals are (...) defended. I conclude that the case for the first premise of the argument from underdetermination is very strong. The disposition of the argument itself depends on the fate of the second premise. (shrink)

Jean Perrin’s argument for the existence of molecules from his 1908 experimental determination of Avogadro’s number raises two questions considered in this article. One is historical: Why as late as 1908 should Perrin have thought it necessary to argue that molecules exist? The other, which takes up the bulk of this article, is philosophical: In view of the fact that his argument appears to assume the existence of molecules as a premise, how, if at all, can a charge of circularity (...) be avoided? I criticize attempted reconstructions of his argument by Salmon, Glymour, and hypothetico-deductivists. And I propose a probabilistic solution that avoids circularity. Finally, I consider whether Perrin’s reasoning, so construed, is an empirical argument for scientific realism. (shrink)