nothing can be said truly about that, which does not exist
Terms express concepts in their ordinary use. They denote concepts in the contexts of propositional attitudes. This analysis agrees with Frege and the Stoics, whereby, in the words of Alonzo Church, nothing can be said truly about that, which does not exist. As the Eleatic Stranger taunts Theaetetus, ὅτι μάλιστα δύνασαι συντείνας πειράθητι, μήτε οὐσίαν μήτε τὸ ἓν μήτε πλῆθος ἀριθμοῦ προστιθεὶς τῷ μὴ ὄντι, κατὰ τὸ ὀρθὸν φθέγξασθαί τι περὶ αὐτοῦ, try with might and main to say something correctly about not-being, without attributing to it either existence or unity or plurality. (Plato, Sophist, 239b)