First a rather imprecise, but nonetheless significant distinction. Some relations can be called material, in that they consist of a tangible concrete relationship between particular things; other relations are more formal, in that they consist of relationships that can exist between abstract as well as concrete things, or alternatively, between only abstract things. Examples of material relations are ‘having the same mass as’ or ‘being in spatio-temporal contact’; examples of formal relations are ‘being larger than’, or ‘having the same number of vertices’. More would have to be said for this distinction to be fully clear, but it is obvious that co-consciousness is a material rather than a formal relation. The relata of co-consciousness are experiences, which are not abstract (even if some people think they are immaterial). Co-consciousness is an experienced relationship between experiences, and as such is a concrete relation between concrete particulars; it is not a relation that can hold between anything other than experiences, and so it is not a relation that can hold between abstract entities.