  In a quantum-Bayesian take on quantum mechanics, the Born Rule cannot be
interpreted as a rule for setting measurement-outcome probabilities from an
objective quantum state. But if not, what is the role of the rule? In this
paper, we argue that it should be seen as an empirical addition to Bayesian
reasoning itself. Particularly, we show how to view the Born Rule as a
normative rule in addition to usual Dutch-book coherence. It is a rule that
takes into account how one should assign probabilities to the consequences of
various intended measurements on a physical system, but explicitly in terms of
prior probabilities for and conditional probabilities consequent upon the
imagined outcomes of a special counterfactual reference measurement. This
interpretation is seen particularly clearly by representing quantum states in
terms of probabilities for the outcomes of a fixed, fiducial symmetric
informationally complete (SIC) measurement. We further explore the extent to
which the general form of the new normative rule implies the full state-space
structure of quantum mechanics. It seems to get quite far.
