In defence of non-ontic accounts of quantum states

The paper discusses objections against non-hidden variable versions of the epistemic conception of quantum states—the view that quantum states do not describe the properties of quantum systems but reflect, in some way to be specified, the epistemic conditions of agents assigning them. In the first half of the paper, the main motivation for the epistemic conception of quantum states is sketched, and a version of it is outlined, which combines ideas from an earlier study of it (Friederich, 2011) with elements of Richard Healey's recent pragmatist interpretation of quantum theory (Healey, 2012). In the second half, various objections against epistemic accounts of quantum states are discussed in detail, which are based on criticisms found in the literature. Possible answers by the version outlined here are compared with answers from the quantum Bayesian point of view, which is at present the most discussed version of the epistemic conception of quantum states.

► Solutions to the paradoxes of quantum theory contrast with dissolutions.
► There are both legitimate and illegitimate uses of anthropocentric notions such as ‘measurement’ in foundational accounts of quantum theory.
► Epistemic accounts of quantum states are not committed to explanatory anti-reductionism.
► Quantum theoretical explanations can be accounted for in non-ontic no less than in ontic accounts of quantum states.