Abstract

There is an extensive philosophical literature on the interrelated issues of identity, individuality, and distinguishability. Out of this discussion has arisen a concept called “permutation invariance” that is asserted to apply to quantum systems. I argue that in fact there is no such invariance, and that the best way to understand the permutation of labels in the symmetrized states is as an exchange of haecceities, rather than as an exchange of essences equivalent to permutation invariance. I argue that the strongest notion of haecceity (i.e., "classical haecceity") does not apply at the quantum level, but that in order to properly account for the need for symmetrization in quantum systems, a weaker kind of haecceity must be involved, which I call quantum haecceity.