 If quantum predicates are relational, they are different from many ordinary relations in that the conditions for the relata are taken as criterial for the application of the term. In this regard one might contrast the relativity of simultaneity with the proposed relativity of position. In relativistic physics specifying a world-line fixes a frame of reference for attributions of simultaneity to events regardless of whether any temporal measurements are being made or contemplated. But in the quantum case, on this proposal, specifying a frame of reference for position (say, the laboratory frame) does not entitle one to attribute position to a system, unless that frame is associated with actually preparing or completing a measurement of position for that system. To be sure, analyzing predicates in terms of occurrent measurement or observation is familiar from neopositivist approaches to the language of science; for example, in Percy Bridgman’s operational analysis of physical terms, where the actual applications of test-response pairs constitute criteria for any meaningful use of a term (see  Theory and Observation in Science ).  Rudolph Carnap’s later introduction of reduction sentences (see the entry on the  Vienna Circle)  has a similar character. Still, this positivist reading entails just the sort of nonlocality that Bohr seemed to abhor.