 The deterministic dynamics (rule 4a) typically does nothing to guarantee that a system will either determinately have or determinately not have a particular property when one observes the system to see whether the system has that property. This is why the collapse dynamics (rule 4b) is needed in the standard formulation of quantum mechanics. It is the collapse dynamics that guarantees that a system will either determinately have or determinately not have a particular property (by the lights of rule 3) whenever one observes the system to see whether or not it has the property. But the linear dynamics (rule 4a) is also needed to account for quantum mechanical interference effects. So the standard theory has two dynamical laws: the deterministic, continuous, linear rule 4a describes how a system evolves when it is not being measured, and the random, discontinuous, nonlinear rule 4b describes how a system evolves when it is measured.