The broadest division of dyadic relations is into those which can only subsist between two subjects of different categories of being (as between an existing individual and a quality) and those which can subsist between two subjects of the same category. A relation of the former kind may advantageously be termed a reference; a relation of the latter kind, a dyadic relation proper.
http://www.commens.org/dictionary/entry/quote-nomenclature-and-divisions-dyadic-relations-2