 On the face of it, it is not difficult to envisage scenarios that would correspond to the diagram in Figure 4. For example, we may take x and y to be the sets {{z}, {z, w}} and {{w},{z, w}}, respectively (i.e., the ordered pairs ⟨z, w⟩ and ⟨w, z⟩), interpreting ‘P’ as the ancestral of the improper membership relation (i.e., of the union of ∈ and =). But sets are abstract entities, and the ancestral relation does not generally satisfy (P.4) (the singleton of the empty set, for instance, or the singleton of any urelement, would have only one proper part on the suggested construal of ‘P’). Can we also envisage similar scenarios in the domain of concrete, spatially extended entities, granting (P.4) in its generality? Admittedly, it is difficult to picture two concrete objects mereologically structured as in Figure 4. It is difficult, for example, to draw two extended objects composed of the same proper parts because drawing something is drawing its proper parts; once the parts are drawn, there is nothing left to be done to get a drawing of the whole. Yet this only proves that pictures are biased towards (P.5). Are there any philosophical reasons to resist the extensional force of (P.5) beyond the domain of abstract entities, and in the presence of (P.4)?