 Many passages in [(Russell 1908)] and [(Whitehead and Russell 1910–13)] may be understood as saying or as having the consequence that the values of propositional functions are sentences. But a coherent semantics of Russell’s formalized language can hardly be provided on this basis (notice in particular, that, since sentences are also substituted for propositional variables, it would be necessary to take sentences as names of sentences.) And since the passages in question seem to involve confusions of use and mention or kindred confusions that may be merely careless, it is not certain that they are to be regarded as precise statements of a semantics. (Church 1976, n.4)