 Despite Lewis’ dismissal, a number of theories appeal to amphibians (i.e., particularized universals lying between particulars and full-fledged universals) or, more precisely, to entities similar to amphibians. Fine (2017) suggests that structural properties should be treated by invoking arbitrary objects (Fine 1985). Davis’ (2014) account of linguistic types as structural properties confronts the problem of the multiple occurrence of one type, e.g., “dog”, in another (e.g., “every dog likes another dog”) (Wetzel 2009). In general, the idea that types are properties of tokens is a natural one, although there are also alternative views on the matter (see entry on  types and tokens).  Be this as it may, Davis proposes that types cannot occur within further types as tokens: they can only occur as subtypes. Therefore, subtypes lie, like amphibians, between types and tokens. Subtypes are individuated by their positions in asymmetric wholes, whereas they are primitively and non-qualitatively distinct in symmetric ones. The approach could be extended to properties such as methane, which would be taken to have four distinct hydrogen subtypes.