  The relationalist might claim that-clauses are ambiguous, and in particular that they pick out different kinds of entities depending on which attitude verb they complement. How do we tell what kinds of entities are picked out? We look at substitution failures. Thus, it might be argued the truth of ‘S remembers that p’ requires that the subject bear the remembering relation to a fact, rather than a proposition. After all, ‘remember’ shows substitution failures for ‘the (true) proposition that p’ but not for ‘the fact that p’.