 These various proposals and developments have arisen in the context of detailed technical investigations. This illustrates two features of the modal approach: on the one hand it makes use of a precise mathematical framework; on the other hand it is flexible and open-ended, and can accommodate different views concerning the rules determining the set of definite-valued observables. It is natural to expect new offshoots; for example, it seems plausible that strategies followed in many-worlds interpretations to define different “branches” can also be incorporated in the modal approach in order to define single-world possibilities. Whatever these prospects, one can at least say that the modal approach has given rise to a fruitful series of investigations into the structure of quantum theory.