Individuality, discernibility, and entanglement

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Based on the sharpened understanding of genuine entanglement as opposed to mere permutation invariance, the Leibniz-strategy has been pursued according to which a traditional version of the principle of the (numerical) identity of (qualitative) indiscernibles can be defended even in the domain of quantum mechanics. This approach has been comprehensively developed in order to do justice to every physically possible situation, bosons in symmetric product states included. Now, the focus turns on the relationship between philosophy of language and metaphysics of physics, in particular concerning the connection between the referencing-problem and the individuality of objects. Due to the performed strategy, the standard-reading of the tensor product indices as (directly referential) proper names is under pressure, but no alternative has been conclusively established. The possible alternatives – referencing via (descriptive) designations, free variables, or (irreducible) demonstratives – will be discussed in detail. This includes to apply the to-use/to-mention distinction which re-appears in the physical distinction of active versus passive symmetry transformations. Also, the modal implications of what is – given a certain description – counterfactually possible should be investigated. The desideratum is a theory of effective reference to physical objects that is broader in scope than quantum mechanics by considering also the quantum field theories. Not only is their formalism label-free, but also are spatial delocalization and vagueness in (so-called) particle number physical facts being relevant for the referencing-problem.