 Both the framework of quasi-set theory and the underlying metaphysics have been extended into the foundations of Quantum Field Theory, where it has been argued, one has non-individual ‘quanta’ (Teller 1995). A form of quasi-set theory may provide one way of formally capturing this notion (French and Krause 2006; for concerns about such a move see Sant’ Anna 2019). It has also been suggested that this offers a way of understanding the sense in which quantum objects may be regarded as vague (French and Krause 2003), although it has been questioned whether vagueness is the appropriate notion here (Darby 2010) and also whether quasi-set theory offers the most perspicuous way of capturing this sense (Smith 2008).  Finally, for those who are leery of quasi-sets and their attendant formal apparatus, there is also the option of returning to Weyl’s original insight, which underpins the quote above, and appropriating his idea of an ‘aggregate’. If this is interpreted non-set-theoretically as an equivalence relation, where the relevant elements are understood as simply objects that have certain properties in common, one can continue to maintain that such objects do not have well-defined identity conditions (Bueno 2019). Indeed, there may be a variety of such frameworks, both formal and metaphysical, in terms of which non-individuality may be understood (Arenhart 2017b). 