  Each scheme of state reconstruction comes down to parametrize the state of a
quantum system by expectation values or probabilities directly measurable in an
experiment. It is argued that the time evolution of these quantities provides
an unambiguous description of the quantal dynamics. This is shown explicitly
for a single spin s, using a quorum of expectation values which contains no
redundant information. The quantum mechanical time evolution of the system is
rephrased in terms of a closed set of linear first-order differential equations
coupling (2s+1)^2 expectation values. This `realization' of the dynamical law
refers neither to the wavefunction of the system nor to its statistical
operator.
