 These entities are often called propositions. Friends of propositions aim both to provide a theory of these entities, and, in so doing, also to solve the two problems for the theory of reference discussed above: (i) the lack of an explanation for the fact that  (5)  is trivial while  (6)  is not, and (ii) the fact (exemplified by  (7)/(8)  and  (9)/(10))  that sentences which differ only in the substitution of expressions with the same reference can differ in truth-value.