WHY MODAL INTERPRETATIONS OF QUANTUM-MECHANICS MUST ABANDON CLASSICALREASONING ABOUT PHYSICAL-PROPERTIES

Modal interpretations of quantum mechanics propose to solve the measur ement problem by rejecting the orthodox view that in entangled states of a system which are nontrivial superpositions of an observable's eig enstates, it is meaningless to speak of that observable as having a va lue or corresponding to a property of the system. Though denying this is reminiscent of how hidden-variable interpreters have challenged ort hodox views about superposition, modal interpreters also argue that th eir proposals avoid any of the objectionable features of physical prop erties that beset hidden-variable interpretations, like contextualism and nonlocality. Even so, I shall prove that modal interpreters of qua ntum mechanics are still committed to giving up at least one of the fo llowing three conditions characteristic of classical reasoning about p hysical properties: (1) Properties certain to be found on measuring a system should be counted as intrinsic properties of the system. (2) If two propositions stating the possession of two intrinsic properties b y the system are regarded as meaningful, then their conjunction should also correspond to a meaningful proposition about the system possessi ng a certain intrinsic property; and similarly for disjunction and neg ation. (3) The intrinsic properties of a composite system should at le ast include (though need not be exhausted by) the intrinsic properties of its parts. Conditions 1-3 are by no means undeniable. But the onus seems to be on modal interpreters to tell us why rejecting one of the se is preferable to an ontology of properties incorporating contextual ism and nonlocality.