The many worlds/many minds formulations of quantum mechanics are reconstructions of Hugh Everett III's (1957a, 1957b, 1973) relative-state formulation of quantum mechanics. Each is presented as a proposal for solving the quantum measurement problem. Much of the philosophical interest in these theories derives from the metaphysical commitments they suggest. They illustrate the roles played by traditional metaphysical distinctions both in formulating and in evaluating physical theories. They also illustrate the range of metaphysical options one must consider if one wants a metaphysics that is consistent with the structure of the physical world suggested by the best physical theories.

The quantum measurement problem is a consequence of the orthodox quantum-mechanical representation of physical properties. In order to account for interference effects, the orthodox view requires that one allows for a physical system to be in...