 A thesis that has a long pedigree but has only recently been gathering attention in the contemporary literature is the “Composition as Identity” thesis. The thesis comes in a weak and a strong form. In its weak form the thesis is that the mereological composition relation is analogous in a number of important ways to the identity relation and so deserves to be called a kind of identity. In its strong form the thesis is that the composition relation is strictly identical with the identity relation, viz. that the parts of a whole are literally (collectively) identical with the whole itself. The strong thesis was considered by Plato in Parmenides and versions of the thesis have been discussed by many historical figures since (Harte 2002, Normore and Brown 2014). The progenitor of the modern version of the thesis is Baxter (1988a, 1988b, 2001) but it is most often discussed under the formulation of it given by Lewis (1991), who first considers the strong thesis before rejecting it in favour of the weak thesis.