  The concept of indistinguishable particles in quantum theory is fundamental
to questions of ontology. All ordinary matter is made of electrons, protons,
neutrons, and photons and they are all indistinguishable particles. Yet the
concept itself has proved elusive, in part because of the interpretational
difficulties that afflict quantum theory quite generally, and in part because
the concept was so central to the discovery of the quantum itself, by Planck in
1900; it came encumbered with revolution. I offer a deflationary reading of the
concept "indistinguishable" that is identical to the Gibbs concept of "generic
phase", save that it is defined for state spaces with only finitely-many states
of bounded volume and energy (finitely-many orthogonal states, in quantum
mechanics). That, and that alone, makes for the difference between the quantum
and Gibbs concepts of indistinguishability. This claim is heretical on several
counts, but here we consider only the content of the claim itself, and its
bearing on the early history of quantum theory rather than in relation to
contemporary debates about particle indistinguishability and permutation
symmetry. It powerfully illuminates that history.
