The reasoning process begins with some initial data, which may reflect some knowledge of the system under discussion or may be purely hypothetical. Here “initial” refers to the beginning of a logical argument, not necessarily to the initial state of a quantum system, though the latter is often included in the initial data. These data must then be expressed in appropriate quantum terms as some sort of property or properties, subspaces of an appropriate Hilbert space, which could be a space of histories, all belonging to a single framework or event algebra, principle R3. Generally there will be more than one framework that can contain the initial data, and the physicist is at liberty to choose among these possibilities, R1. However, the types of conclusions which can be drawn using a particular framework (and thus event algebra) will depend upon the framework, and for this reason the physicist’s interests can, and in general will, influence the choice of framework. It is utility, R4, which determines this choice; from a fundamental point of view all frameworks are equally good, R2.