  We generalize classical statistical mechanics to describe the kinematics and
the dynamics of systems whose variables are constrained by a single quantum
postulate (discreteness of the spectrum of values of at least one variable of
the theory). This is possible provided we adopt Feynman's suggestion of
dropping the assumption that the probability for an event must always be a
positive number. This approach has the advantage of allowing a reformulation of
quantum theory in phase space without introducing the unphysical concept of
probability amplitudes, together with all the problems concerning their
ambiguous properties.
