  The above considerations are typically presented within the ‘orthodox’ interpretation of quantum mechanics but there are a further set of responses which step outside of this. Thus van Fraassen, for example (van Fraassen 1985 and 1991) has advocated a form of ‘modal’ interpretation, in the context of which (standard) PII can be retained. At the core of this approach lies a distinction between two kinds of state: the ‘value’ state, which is specified by stating which observables have values and what they are; and the ‘dynamic’ state, which is specified by stating how the system will develop both if isolated and if acted upon in some definite fashion. The evolution of the latter is deterministic, in accordance with Schroedinger’s equation, but the value state changes unpredictably, within the limits set by the dynamic state (for criticism see some of the papers in Dieks and Vermaas 1998). Because the actual values of observables do not increase predictive power if added to the relevant dynamic state description, they are deemed to be ‘empirically superfluous’. In the case of fermions, at least, distinct value states can be assigned to each particle and PII saved.