 The second formulation of the measurement problem, though basically equivalent to the first, raises an important question: Can Bohmian mechanics itself reconcile these two dynamical rules? How does Bohmian mechanics justify the use of the “collapsed” wave function instead of the original one? This question was answered in Bohm’s first papers on Bohmian mechanics (Bohm 1952: Part I, Section 7 and Part II, Section 2). What would nowadays be called effects of decoherence, produced by interaction with the environment (air molecules, cosmic rays, internal microscopic degrees of freedom, etc.), make it very difficult for significant overlap to develop between the component of the after-measurement wave function corresponding to the actual result of the measurement and the other components of the after-measurement wave function. (This overlap refers to the configuration space of the very large system that includes all systems with which the original system and apparatus come into interaction.) But without such overlap that component all by itself generates to a high degree of accuracy the future evolution of the configuration of the system and apparatus. The replacement is thus justified as a practical matter (see also Dürr, Goldstein &amp; Zanghì 1992a: Section 5).