 The problem here is said to be that the substitution of “true proposition” for “fact” or vice versa generates different readings (in particular, readings with different truth-values). Suppose Daniel has to memorize a list of true propositions, of which one is the proposition that this is a leap year. Then it is contended that we can easily imagine a scenario in which (17) and (18) differ in truth-value. Another way of putting the same point might be to say that (17) is equivalent to