Abstract
Von Neumann's statistical theory of quantum measurement interprets the instantaneous quantum state and derives instantaneous classical variables. In reality, quantum states and classical variables coexist and can influence each other in a time-continuous way. This has been motivating investigations since a long time in quite different fields from quantum cosmology to optics as well as in foundations. Different theories (mean-field, Bohm, decoherence, dynamical collapse, continuous measurement, hybrid dynamics, etc.) emerged for what I call 'coexistence of classical continuum with quantum'. I apply to these theories a sort of 'free will' test to distinguish 'tangible' classical variables useful for causal control from useless ones.
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