 If Fregean descriptivism is true, and “the greatest philosopher of antiquity” is indeed the description I associate with the name “Aristotle”, then it seems that (21) and (22) must be a pair of sentences which differ only via the substitution of expressions (the italic ones) with the same content. If this is right, then (21) and (22) must express the same proposition, and have the same truth-value. But this seems to be a mistake; while (21) appears to be true (Aristotle could hardly have failed to be himself), (22) appears to be false (perhaps Aristotle could have been a shoemaker rather than a philosopher; or perhaps if Plato had worked a bit harder, he rather than Aristotle could have been the greatest philosopher of antiquity).