  The paper proves that quantum mechanics is compatible with the constructive
realism of modern philosophy of science. The proof is based on the observation
that properties of quantum systems that are uniquely determined by their
preparations can be assumed objective without the difficulties that are
encountered by the same assumption about values of observables. The resulting
realist interpretation of quantum mechanics is made rigorous by studying the
space of quantum states---the convex set of state operators. Prepared states
are classified according to their statistical structure into indecomposable and
decomposable instead of pure and mixed. Simple objective properties are defined
and showed to form a Boolean lattice.
