 Turning to asymmetry, Bliss (2014) and Thompson (2016, 2018) critically assess the general theoretical motivations for thinking that grounding is asymmetric and propose potential counterexamples. Thompson suggests that, given the functional relationship between mass, volume, and density (the density of a substance is its mass divided its volume), we should accept that, say, [g has 3cm3 volume] grounds [g has 2g/cm3 density] and vice versa. It’s worth noting, however, that many reciprocal functional relationships don’t involve symmetric grounding. As Alexander Skiles has suggested to us in conversation, there is, for example, a reciprocal functional relationship between how many things are Socrates and how many members Socrates’ singleton has, but it’s clear in which direction the grounding runs in this case.