  The Proper Name Theory nicely accommodates (BQ1)–(BQ3); that is, on this theory we see why co-referential expressions cannot be substituted for one another. According to the Proper Name Theory, the name ‘Cicero’ does not occur in ‘‘Cicero’’; from the mere fact that Cicero = Tully, it does not follow that  ‘Tully’ can be substituted for ‘Cicero’ in ‘‘Cicero’’. As Quine puts it, ‘[t]o make substitution upon a personal name, with such a context, would be no more justifiable than to make a substitution upon the term ‘cat’ within the context ‘cattle’ (Quine 1961, p. 141). The Proper Name Theory permits the creation of new quotations much as natural languages permit the introduction of new names. And it prohibits quantifying in, since each quotation is a single word, and so there is nothing to quantify into. To see that this is so, think of the left and right quotation marks as the 27th and 28th letters of the roman alphabet; in that case quantifying into (4) in deriving (9) makes as much sense as deriving (16) from (14) and (15) by quantifying into (14):