Sometimes a theory is interpreted realistically--i.e., as literally true--whereas sometimes a theory is interpreted instrumentalistically--i.e., as merely a convenient device for summarizing, systematizing, deducing, etc., a given body of observable facts. This paper is part of a program aimed at determining the basis on which scientists decide on which of these interpretations to accept a theory. I proceed by examining one case: the nineteenth-century debates about the existence of atoms. I argue that there was a gradual transition from an instrumentalist (...) to a realistic acceptance of the atomic theory, because of gradual increases in its predictive power, the "testedness" of its hypotheses, the "determinateness" of its quantities, and because of resolutions of doubts about the acceptability of its basic explanatory concepts. (shrink)

Putnam and Finkelstein have proposed the abandonment of distributivity in the logic of quantum theory. This change results from defining the connectives, not truth-functionally, but in terms of a certain empirical ordering of propositions. Putnam has argued that the use of this ordering ("implication") to govern proofs resolves certain paradoxes. But his resolutions are faulty; and in any case, the paradoxes may be resolved with no changes in logic. There is therefore no reason to regard the partially ordered set of (...) propositions as a logic--i.e. as embodying a criterion for soundness of proofs. Its role in quantum theory ought to be understood in an entirely different way. (shrink)

Suppose that two theories θ and θ ′ are observationally equivalent, so that any possible evidence for or against one has the same relation to the other. Are these theories then logically equivalent? If not, is rational choice between them possible (on non-empirical grounds), or must we forever suspend judgment? It is argued that these questions are unintelligible, because the required sense of "observationally equivalent" does not exist. An explanation as to why this fact has been long overlooked is attempted (...) by suggesting that the existence of a precisely describable "domain" for θ and θ ′ frequently makes discussion of observational equivalence possible, though not in the sense required by the above questions. (shrink)