 Perfect naturalness is generally understood to be definable in terms of relative naturalness: a property is perfectly natural just in case no property is more natural than it. But Lewis also held that relative naturalness could be defined in terms of perfect naturalness: \(F\) is more natural than \(G\) just in case \(F\) has a shorter and less complex definition in terms of perfectly natural properties than \(G\) (Lewis  1986b,  61). Here, a “definition” of a property can be understood as an expression referring to that property in a formal language which only has simple predicates expressing perfectly natural properties (in addition to certain logical resources which allow complex predicates to be constructed out of these simple  ones).[3]  This claim has been controversial even among naturalness enthusiasts. One influential worry (raised in Sider  1995)  is that many of the properties we are interested in, and between which we need to draw distinctions of naturalness (e.g. greenness and grueness), will only have infinite definitions in terms of the perfectly natural properties, so that they will all come out equally  natural.[4]  Nevertheless, length and complexity of definitions has been broadly accepted at least as a heuristic guide. For example, someone who held that adjacency and chargedness were perfectly natural would be expected to hold that being adjacent to something charged is more natural than being adjacent to an uncharged thing that is adjacent to something charged.