 Secondly, there is an interesting class of entities that are fundamental according to  (AI),  but may cause trouble for other views about fundamentality. These entities are sometimes known as “idlers” (e.g., Lewis 2009: 205; Bennett 2017: 123). For Lewis, idlers are fundamental properties, which are instantiated in the actual world, but “play no active role in the workings of nature”. So, idlers are at least causally isolated. However, we can further postulate that “absolute idlers” are absolutely isolated: they depend on nothing, and nothing, at least nothing concrete, depends on them. Absolute idlers would thus be absolutely independent in the sense required by (AI). Whether there are any such absolute idlers is of course another question. If there are any absolute idlers, they are rather uninteresting entities—indeed, they are presumably completely beyond our ken given their isolation. Moreover, for the idea of absolute idlers to have any plausibility, we would have to restrict their isolation in such a way that they may participate in abstract constructions such as sets.