In Interpreting Quantum Theories, Ruetsche argues that the occurrence of unitarily inequivalent representations in quantum theories with infinitely many degrees of freedom poses a novel interpretational problem. According to Ruetsche, such theories compel us to reject the so-called ideal of pristine interpretation; she puts forward the ‘coalescence approach’ as an alternative. In this article I offer a novel defence of the coalescence approach. The defence rests on the claim that the ideal of pristine interpretation already fails before one considers the peculiarities of QM∞: there are pre-QM∞ parallels to coalescence. Despite this departure from pristinism, the ‘modest’ view that emerges poses no threat to scientific realism.
Idealization presents well known problems for realist views of theories: truth cannot be what we want in our theories if we knowingly introduce falsity into our theoretical treatments. One attractive defence of realism has it that, although idealized models themselves falsely represent their subjects, they stand in for intractable exact treatments in the theoretical deductions from true premises that constitute explanations and predictions. In this paper I will argue that on this proxy view of idealized models, certain relations are to be expected between theory and model, relations that fail to hold between quantum mechanics and its applications in quantum chemistry. What is needed is a view of what makes a molecular model a good one that is independent of its relation to some exact treatment.