  Bohmian mechanics and the Ghirardi-Rimini-Weber theory provide opposite
resolutions of the quantum measurement problem: the former postulates
additional variables (the particle positions) besides the wave function,
whereas the latter implements spontaneous collapses of the wave function by a
nonlinear and stochastic modification of Schr\"odinger's equation. Still, both
theories, when understood appropriately, share the following structure: They
are ultimately not about wave functions but about ``matter'' moving in space,
represented by either particle trajectories, fields on space-time, or a
discrete set of space-time points. The role of the wave function then is to
govern the motion of the matter.
