  The Bayesian approach to quantum mechanics of Caves, Fuchs and Schack is
presented. Its conjunction of realism about physics along with anti-realism
about much of the structure of quantum theory is elaborated; and the position
defended from common objections: that it is solipsist; that it is too
instrumentalist; that it cannot deal with Wigner's friend scenarios. Three more
substantive problems are raised: Can a reasonable ontology be found for the
approach? Can it account for explanation in quantum theory? Are subjective
probabilities on their own adequate in the quantum domain? The first question
is answered in the affirmative, drawing on elements from Nancy Cartwright's
philosophy of science. The second two are not: it is argued that these present
outstanding difficulties for the project. A quantum Bayesian version of Moore's
paradox is developed to illustrate difficulties with the subjectivist account
of pure state assignments.
