  There is a significant body of literature, which includes Itamar Pitowksy's
"Betting on Outcomes of Measurements," that sheds light on the structure of
quantum mechanics, and the ways in which it differs from classical mechanics,
by casting the theory in terms of agents' bets on the outcomes of experiments.
Though this approach, by itself, is neutral as to the ontological status of
quantum observables and quantum states, some, notably those who adopt the label
"QBism" for their views, take this approach as providing incentive to conclude
that quantum states represent nothing in physical reality, but, rather, merely
encode an agent's beliefs. In this chapter, I will argue that the arguments for
realism about quantum states go through when the probabilities involved are
taken to be subjective, if the conclusion is about the agent's beliefs: an
agent whose credences conform to quantum probabilities should believe that
preparation procedures with which she associates distinct pure quantum states
produce distinct states of reality. The conclusion can be avoided only by
stipulation of limitations on the agent's theorizing about the world,
limitations that are not warranted by the empirical success of quantum
mechanics or any other empirical considerations. Subjectivists about quantum
probabilities should be realists about quantum states.
