of quantum states, one could well regard this result as a reductio of the epistemic conception of states itself. The main problems with this conclusion are, first, that in quantum theoretical practice there is virtually always agreement on which observable some value measured in some setup is a value of, and it seems difficult to imagine how quantum theory could be as empirically successful as it is if this were not the case. Second, if there were no fact of the matter as to which observable some measured value is a value of, there could never be any knowledge of the values of observables, at least not knowledge obtained in experiment. It seems clear, however, that physicists often do have knowledge of the values of at least some observables, and this makes the idea that there is no determinate answer to the question of which observable is measured in which setup even more problematic.[^17] The account presented in the following subsection of this paper can be seen as an attempt to improve on quantum Bayesianism in precisely these respects.

The Rule Perspective
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### Quantum state assignment

As I have argued, quantum Bayesianism’s denial of the assumption that there can 