  The concept of probability was prominent in the original foundations of
quantum mechanics, and continues to be so today. Indeed, the controversies
regarding objective and subjective interpretations of probability have again
become active. I argue that, although both objective and subjective
probabilities have domains of relevance in QM, their roles are quite distinct.
Even where both are legitimate, the objective and subjective probabilities
differ, both conceptually and numerically. There are quantum probabilities that
have no useful subjective interpretations, and there are subjective
probabilities that cannot be realized as quantum probabilities.
