This Chapter develops a realist information-theoretic interpretation of the

nonclassical features of quantum probabilities. On this view, what is

fundamental in the transition from classical to quantum physics is the

recognition that \emph{information in the physical sense has new structural

features}, just as the transition from classical to relativistic physics rests

on the recognition that space-time is structurally different than we thought.

Hilbert space, the event space of quantum systems, is interpreted as a

kinematic (i.e., pre-dynamic) framework for an indeterministic physics, in the

sense that the geometric structure of Hilbert space imposes objective

probabilistic or information-theoretic constraints on correlations between

events, just as the geometric structure of Minkowski space in special

relativity imposes spatio-temporal kinematic constraints on events. The

interpretation of quantum probabilities is more subjectivist in spirit than

other discussions in this book (e.g., the chapter by Timpson), insofar as the

quantum state is interpreted as a credence function---a bookkeeping device for

keeping track of probabilities---but it is also objective (or intersubjective),

insofar as the credences specified by the quantum state are understood as

uniquely determined, via Gleason's theorem, by objective correlational

constraints on events in the nonclassical quantum event space defined by the

subspace structure of Hilbert space.