 There are also several specifically philosophical issues connected to the modal program: about the nature of the “things” to which quantum mechanics refers, that is, about the basic categories of the quantum ontology. As we have seen, in general the properties of quantum systems are considered to be monadic in modal interpretations, with the exception of the perspectival version PMI where these properties are relational. In both cases, it may be asked whether a quantum system has to be conceived as an individual substratum supporting properties or as a mere “bundle” of properties which do not need to constitute an individual in the ordinary sense. Following an original idea of the MHI, da Costa, Lombardi and Lastiri (2013) and da Costa and Lombardi (2014) have suggested that, in the modal context, the bundle view is the most appropriate one to supply an answer to the problem of indistinguishability of identical quantum particles (French and Krause 2006). As noticed by Steven French (2020 [Other Internet Resources]), this view of non-individual bundles finds a natural resonance with ontic structural realism, which was mainly motivated by the ontological challenges of quantum mechanics (Ladyman 1998). Moreover, this ontology of properties has been taken as a basis for a metaphysical interpretation of relational quantum mechanics (Oldofredi 2021). It should be noted that this bundle ontology does not contradict the emergence of classical distinguishable particles in certain situations, e.g. the classical limiting case (Lombardi and Dieks 2016).